Written by Sig Silber

HEADLINES (Updated 5:59 PM EST) –

– Major winter storm poised to bring heavy snow and areas of freezing rain to the Mid-Atlantic and Northeast beginning on Wednesday

– Snow over the central Plains expected to taper off tonight

– More unsettled weather will impact the Pacific Northwest over the next couple of days

This article provides continuous updates for a variety of Weather and Weather-Related Threats as well as a general weather forecast. These are “Live” maps that continually update. Please pay attention to the Mesoscale Events maps — Mesoscale Events are potentially life-threatening situations.

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For those interested in longer-term forecasts, we just published the new NOAA Seasonal Outlook and it can be accessed here.

Directory

CONUS Focal Points

Short Range Focal Points

Short Range Forecast Discussion NWS Weather Prediction Center College Park MD – 300 PM EST Tue Dec 15 2020

Valid 00Z Wed Dec 16 2020 – 00Z Fri Dec 18 2020

…Major winter storm poised to bring heavy snow and areas of freezing rain to the Mid-Atlantic and Northeast beginning on Wednesday…

…Snow over the central Plains expected to taper off tonight…

…More unsettled weather will impact the Pacific Northwest over the next couple of days…

An area of low pressure currently developing under an energetic upper trough over Texas will take center stage as it is forecast to track across the East Coast and evolve into a significant nor’easter. The developing system is expected to produce moderate snowfall across portions of the central Plains into this evening. Slick road conditions and reduced visibility at times could make travel difficult across the region where Winter Storm Warnings and Winter Weather advisories are in effect into this evening.

As this low pressure system moves generally eastward, moisture from the Gulf of Mexico and eventually from the Atlantic Ocean will interact with the upper trough and result in a swath of rain to quick expand across the Deep South, the Southeast and into the Mid-Atlantic on Wednesday. Meanwhile, a strong area of high pressure located over southern Quebec, Canada will help filter colder air down along of the Appalachian Mountains into the Mid-Atlantic. This will result in an expanding area of snow to overspread the Ohio Valley and into the central Appalachians on Wednesday. In between the snow in the north and the rain in the south, a wintry mix is forecast to stretch across the southern Appalachians and the interior Mid-Atlantic roughly along the I-95 corridor. Freezing rain is the main concern across this region, as upwards of a quarter inch of ice accretion is possible. This could lead to scattered tree damage and power outages. As the precipitation shield advances north throughout the day on Wednesday, heavy snow will overtake areas northwest of I-95 in the Mid-Atlantic. This means major cities, such as Washington D.C. and Philadelphia, will likely see a wintry mix and potentially plain rain for areas just to the southeast. Further northeast, heavy snow will also encroach upon northern New Jersey southern New York State by Wednesday evening, this includes the greater New York City metro region with strengthening winds from the northeast. By Wednesday night, snow will also impact southern New England as the storm will likely near peak intensity while moving off the coast south of Long Island. The heaviest snowfall amounts are currently forecast across south-central Pennsylvania, where as much as two feet of snow is possible. This would likely lead to very dangerous travel conditions and isolated power outages. Many locations from eastern West Virginia to southeast Massachusetts to forecast to see a foot of snowfall accumulation. Snowfall amounts are expected to drop off dramatically to the south and east as sleet and rain are expected to mix in. There is still uncertainty regarding exact alignment of the rain/snow line. A very slight adjustment to the north or south could mean for vastly different outcomes in local areas from central Maryland to Long Island. Be sure to check your local forecast for the latest updates and more specific details.

Meanwhile, the Pacific Northwest will see their own unsettled weather through the next couple of days as two separate systems swing across the region. The current wave of moisture associated with a frontal system will quickly penetrate well inland into the northern and central Rockies by Wednesday morning before a stronger storm brings the next wave of coastal rain and mountain snow by Wednesday evening. Rainfall amounts of 1 to 2 inches are likely during this time frame along the immediate coastline. Across the Cascade Mountains and higher elevations of Idaho and northwest Montana, 1 to 2 feet of snow could fall.

We try to keep this up to date but if is not you can find the updated version here.

When you click on this image it takes you to the SPC Fire Warning Page and you get a set of maps for Days 1, 2, 3 – 8, etc. You can then click on those for more detailed information. The map is a bit blurry as I tried to make it a bit larger than the map provided by NOAA but should be able to see where the current wildfire risks are. But if you click on this map, you will get to see three maps that show the risk for different time periods.

Thunderstorm Risk

This should play out something like shown in this 60 Hour Forecast Animation

Here is a national animation of weather fronts and precipitation forecasts with four 6-hour projections of the conditions that will apply covering the next 24 hours and a second day of two 12-hour projections the second of which is the forecast for 48 hours out and to the extent it applies for 12 hours, this animation is intended to provide coverage out to 60 hours. Beyond 60 hours, additional maps are available at links provided below. The explanation for the coding used in these maps, i.e. the full legend, can be found here although it includes some symbols that are no longer shown in the graphic because they are implemented by color-coding.

The two maps below break it down by day and may be easier to read.

Now, the Day One and Two CONUS Forecasts: These Maps Update Daily.

Day One CONUS Forecast	Day Two CONUS Forecast
These graphics update and can be clicked on to enlarge. You can see where the weather will be

During the winter much of our weather originates in the Pacific. That is why we pay attention to the near-term history of storms arriving.

Temperature

A version that shows a 20 hour animation and some other views can be found here

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Day 3 – 7 Hazards

Valid Friday December 18 2020 – Tuesday December 22 2020

Hazards:

– Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great Basin, Sat-Mon, Dec 19-Dec 21.

– Flooding possible across portions of the Pacific Northwest.

– Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Sat-Mon, Dec 19-Dec 21.

– Heavy snow across portions of the Northern/Central Rockies, Sun-Mon, Dec 20-Dec 21.

– High winds across portions of the Northern/Central Rockies and the Northern/Central Plains, Sat-Sun, Dec 19-Dec 20.

– Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Sat, Dec 19.

– Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Fri-Sat, Dec 18-Dec 19.

– High winds across portions of mainland Alaska, Fri, Dec 18 and Mon-Tue, Dec 21-Dec 22.

– Much below normal temperatures across portions of mainland Alaska, Fri-Tue, Dec 18-Dec 22.

– Heavy precipitation across portions of the Eastern Aleutians and mainland Alaska, Mon-Tue, Dec 21-Dec 22.

Detailed Summary:

Throughout the medium range period (Friday, Dec 18 – Tuesday, Dec 22), hazards affecting the continental United States will occur mainly in the Northwest. From Saturday through Monday a series of upper-level troughs are forecast to drive multiple frontal systems and the moisture they carry onshore from the northeast Pacific, fueling a near constant flow of heavy precipitation to northern California and the Pacific Northwest. While lower elevations closer to the coast will likely feel this precipitation as heavy rain, heavy snow should fall at higher elevations along the Coastal Ranges and Oregon/Washington Cascades. As these systems move further inland, they are expected to produce heavy snow over the Northern Rockies and Wind River Mountains/Tetons over the weekend and into Monday. Moderately gusty winds may accompany the frontal system passing through the Pacific Northwest late Saturday into early Sunday, however these winds are anticipated to remain non-hazardous. Conversely, as the same system passes over the Rockies and into the Plains the winds will pick up, producing strong enough gusts in Montana, Wyoming, and portions of northern Colorado that they may be hazardous.

To the East, a low pressure/frontal system is forecast to drop from the Central to the Southern Plains Friday into Saturday, bringing with it the potential to produce heavy rain along the Gulf Coast from eastern Texas to western Louisiana. Additionally, throughout the entire period temperatures in the Plains and Mississippi Valley are expected to be anywhere from 10 to 25 degrees above normal, with Sunday and Monday forecast to have the largest and most widespread departures. Though anomalous, these temperatures are not expected to be hazardous.

Similarly to the Northwest CONUS, Alaska will have a full plate of hazards as well. On Friday, a strong high pressure system over the Arctic Ocean opposed by a deep low positioned in the Gulf of Alaska will set up a strong pressure gradient over the Mainland, creating the potential for a high wind hazard over the central Interior. The same low pressure system is forecast to bring heavy precipitation to the Panhandle and eastern Southcentral near the coast throughout the beginning of the weekend. At the start of next week another very deep low pressure system is forecast to move eastward through the Bering Sea. As upper level disturbances as well as the fronts associated with this system approach the western coastline, it is expected to bring high winds to the Southwest Mainland as well as heavy precipitation from the eastern Aleutians to the Kenai Peninsula. Throughout the period much of the state will likely experience much below average high and low temperatures. While this is not much of a concern for the highs, much below average lows can be hazardous, as they pose a risk to health and safety if there is prolonged exposure. The most severe departures from normal are forecast for the Central and Eastern Interior, where temperatures are expected to reach as low as -35 to -40F.

(This is updated only during the week) Note the first list is weather highlights, this list is hazards. Not sure there is that much of a difference but they come from two different parts of NOAA. The Day 3 – 7 Hazards List does not update on weekends. But it is still useful as it remains valid for the period of time it covers. Of course, all forecasts are subject to change. Later we show a map of the hazards. Perhaps we should show them together.

Click here for the latest complete Day 3 -7 Hazards forecast which updates only on weekdays. It includes the full discussion which I do not update in this article but only present the highlights.

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Ski Snow Reports

New Feature – Ski Reports. (We may be a tad premature but not by much). It is difficult to find reports that auto-update on-screen (and they are very long) but these links will get you to them – If you have additional suggestions make them in the comments section after every GEI Article and we may add those links. We will try to not have too much overlap as that can add to the confusion.

We will update the above map weekly but more frequent updates can be obtained here.

Snow Forecasts.

Day 1

Day 2

Additional snow information can be found here and here.

We also include drought information in this section.

New December Drought Outlook

Seasonal Outlook Issued November 19, 2020

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Tropical Events

I am replacing the large with three small maps but you can click on them to get larger versions. Even though they are small maps you should be able to tell if there is activity and If I see activity I will make the map where there is activity full size and when available add other related maps.

the Central Pacific.	the Eastern Pacific	the Atlantic and the Gulf of Mexico

Atlantic and Gulf of Mexico

And the Eastern Pacific

Updates on individual named storms can be obtained here.

And the Western Pacific

Weekly Tropical Forecast

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Intermediate-Term Weather Forecast

And shifting to the Alaska and CONUS Intermediate-Term Weather Forecast showing from left to right, Days 1- 5, 6 – 10, 8 – 14 and Weeks 3 – 4 You can click on these maps to have them enlarge, there are larger versions in the Addendum (More Weather the link is shown at the end of this section, and there are larger versions of these maps in the Addendum. Also, the discussions that go with these forecast maps can be found here (first two weeks) and here (Weeks 3 and 4).

First Temperature

And then Precipitation

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Mesoscale Events

The following map shows where mesoscale events are occurring or forecast. If you do not see any areas highlight on this map than there are no mesoscale events taking place or forecast. A mesoscale event is a very serious situation for a very small area and detailed information is provided for these events when they occur or are forecast. If a mesoscale event is shown, click on the map and more detail on the event will be shown.

Two different parts of the NWS issue this map and they are not always in agreement although they are pretty close. They (Norman Oklahoma and College Park Maryland) issue the alerts when they realize the need, so it is best to look on both maps and click one or both if you see areas highlighted.

This next map showing where “Headlines” have been issued for convection (and an animation of the recent movement of storms) should update and you should be able to click on to get additional details but if it does not update when you click on it, click here.

There is a slight difference between convection and thunderstorms. The below map shows where “Headlines” have been issued for Thunderstorms. You should be able to click on the map to get additional details but if it does not update, you can click here.

The map below shows the current wildfire risk which becomes more significant as we move into Summer. When you click on this image it takes you to the SPC Fire Warning Page and you get a set of maps for Days 1, 2, 3 – 8, etc. You can then click on those for more detailed information. The map is a bit blurry as I tried to make it a bit larger than the map provided by NOAA but should be able to see where the current wildfire risks are. But if you click on this map, you will get to see three maps that show the risk for different time periods.

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Now the Day 3 – 7 Hazards Outlook Maps

The orange and red outlined areas are what is most concerning of the forecasted Day 3 – 7 Hazards. This graphic does not update during the weekend. There is a discussion that goes with this graphic and you can access that discussion here.

The following is provided to help the reader relate the maps to how NWS will describe an area of the U.S.

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Now to our More Detailed Weather Report

This graphic is about Atmospheric Rivers i.e. thick concentrated movements of water moisture. More explanation on Atmospheric Rivers can be found by clicking here or if you want more theoretical information by clicking here. The idea is that we have now concluded that moisture often moves via narrow but deep channels in the atmosphere (especially when the source of the moisture is over water) rather than being very spread out. This raises the potential for extreme precipitation events.

500 MB Mid-Atmosphere View

The map below is the mid-atmosphere 3-Day chart rather than the surface highs and lows and weather features. In some cases, it provides a clearer less confusing picture as it shows only the major pressure gradients. This graphic auto-updates so when you look at it you will see NOAA’s latest thinking. The speed at which these troughs and ridges travel across the nation will determine the timing of weather impacts. This graphic auto-updates I think every six hours and it changes a lot. Thinking about clockwise movements around High-Pressure Systems and counterclockwise movements around Low-Pressure Systems provides a lot of information.

Day 3 Above, 6 Below	Day 4 Above,7 Below	Day 5 Above.

Here are the precipitation forecasts. First the cumulative for Days 1 – 3

Then cumulative for Days 1 – 5

Then cumulative for Days 1 – 7

Now we look at the forecast for the Maximum Temperature three days out.

Looking ahead to next week.

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Additional Tools to Obtain Watches and Warnings

Below you will see a number of different maps that are updated in real-time, making this a “live” report. If a part of one or more of the maps shows an area that is highlighted, you can click on it and get the full current report. By having the reader click on these active situations rather than having GEI do so, you will not miss any events in which you might have an interest and which we had not noticed and the page will not get cluttered with warnings, etc that have since expired.

Our focus here is events that are likely to last in the range of six hours but there can be longer or shorter events that are addressed by the Storm Prediction Center which is the main source of the information in this article. Long-term major events like a Hurricane are more likely to be in a separate article. But that may not always be the case. Since in general, all the links on this page transfer you into the NOAA system, in order to get back into this article you need to either close the tab to which you were transferred or click back on the tab that has this article.

Live Warning Maps which If Severe Weather is Shown can be Clicked on to get more detail about these events. If there is a current warning shown on the map, click on the map for additional information related to the event.	These maps are updated as risks are identified.
This is the current graphic showing any mesoscale discussions (MD’s) which are in effect over the contiguous United States. Please read the description of the purpose of our MD’s for further information. Details on all valid MD’s may be found on our Current Mesoscale Discussions page.
Convective Outlooks
This is today’s forecast for organized severe thunderstorms over the contiguous United States. Please read the description of the risk categories for further information. You may find the latest Day 1 Outlook available as well as all Outlooks issued today online.	Today’s Outlook
This is tomorrow’s forecast for organized severe thunderstorms over the contiguous United States. Please read the description of the risk categories for further information. The latest Day 2 Outlook is available as well as all Outlooks that have been issued today.	Tomorrow’s Outlook
This is the day after tomorrow’s (day 3) forecast for organized severe thunderstorms over the contiguous United States. Please read the description of the risk categories for further information. The latest Day 3 Outlook is available as well as all Outlooks that have been issued today.	Day 3 Outlook
This is the day 4-8 forecast for organized severe thunderstorms over the contiguous United States. The latest Day 4-8 Outlook is available as well as all Outlooks that have been issued today. Note: A severe weather area depicted in the Day 4-8 period indicates a 30% or higher probability for severe thunderstorms (e.g. a 30% chance that a severe thunderstorm will occur within 25 miles of any point).	Day 4-8 Outlook
The Thunderstorm Outlooks depict the probability of thunderstorms across the contiguous United States in 4 or 8 hour time periods. The probabilistic forecast directly expresses the best estimate of a thunderstorm occurring within 12 miles of a point. The three probabilistic forecast thresholds are 10, 40, and 70 percent.	Thunderstorm Outlook
Fire Weather Outlooks
This is today’s forecast for organized wildfires over the contiguous United States. Please read the description of the risk categories for further information about this product.	Today’s Outlook
This is tomorrow’s forecast for organized wildfires over the contiguous United States. Please read the description of the risk categories for further information about this product.	Tomorrow’s Outlook
This is day 3-8 forecast for organized wildfires over the contiguous United States. Please read the description of the risk categories for further information about this product.	Day 3-8 Outlook

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