Written by Sig Silber

HEADLINES (Updated 5:05 PM EST) –

– A swath of light to moderate snow is likely from the central Rockies to the central Great Lakes through Saturday before impacting northern Maine by Saturday night

– A lull in the rain and snow expected on Saturday for the Pacific Northwest and northern California before the next round arrives Saturday night

– More snow will traverse the central/southern Rockies through Saturday, reaching the central Plains by Sunday with some mixed precipitation

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.

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CONUS Focal Points

Short Range Focal Points

Short Range Forecast Discussion NWS Weather Prediction Center College Park MD – 313 PM EST Fri Dec 11 2020

Valid 00Z Sat Dec 12 2020 – 00Z Mon Dec 14 2020

…A swath of light to moderate snow is likely from the central Rockies to the central Great Lakes through Saturday before impacting northern Maine by Saturday night...

…A lull in the rain and snow expected on Saturday for the Pacific Northwest and northern California before the next round arrives Saturday night…

…More snow will traverse the central/southern Rockies through Saturday, reaching the central Plains by Sunday with some mixed precipitation…

A low pressure system is forecast to intensify and move across the Midwest into the lower Great Lakes through Saturday. This system will produce a swath of snow and mixed precipitation from the central Plains through the central Great Lakes. Meanwhile, moisture drawn from the Gulf of Mexico will be lifted ahead of a trailing cold front, fueling showers and thunderstorms across the Arklatex region and Lower Mississippi Valley through tonight. As the storm center moves towards the lower Great Lakes on Saturday, moderate to heavy snow is forecast to develop over the northern part of lower Michigan while mixed rain and snow develops over northern New England. Total snowfall amounts of around 3 to 6 inches are forecast from southeast Nebraska to southern Wisconsin, with locally higher amounts possible. The highest snowfall is likely to occur across the northern part of lower Michigan, where 6 to 12 inches of snow with locally higher amounts is forecast. This amount of snow will likely lead to treacherous travel across the region. The snow over lower Michigan will quickly taper off Saturday night as the storm center tracks towards northern New England. 6 to 8 inches of snowfall can be expected for northern Maine with mixed precipitation farther south across interior northern New England through Sunday.

Ahead of the storm, widespread southerly winds will allow temperatures to become 10 to 20 degrees above average over the country’s eastern third. In comparison, parts of the central and southern High Plains will be 10 to 15 degrees below average.

High elevation snow will continue over the Pacific Northwest and Intermountain West through tonight. But as the associated upper trough moves farther inland, a lull in the precipitation is expected to settle across the region on Saturday before the next surge of moisture arrives Saturday night and continues into Sunday. The biggest impact along the West Coast will be potentially heavy rain along coastal regions of northern California and Oregon. Total rainfall amounts could locally reach 4 inches and could lead to isolated flooding. Upwards of two feet of snow could fall across the Sierra and Cascade mountain ranges as well.

The aforementioned upper trough is expected to move into the southern Rockies by Saturday evening and into the southern Plains by Sunday. Light to moderate snow will be spreading across the central/southern Rockies behind the upper trough. A low pressure system will develop and move across the southern Plains on Sunday, spreading wintry weather across the central Plains Sunday morning north of the storm track. By Sunday evening, rain and some thunderstorms associated with the system are expected to expand across the Deep South towards the interior Southeast.

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 Monday December 14 2020 – Friday December 18 2020

Hazards:

– Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great Basin, Tue-Fri, Dec 15-Dec 18.

– Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Tue-Fri, Dec 15-Dec 18.

– Heavy precipitation across portions of the Mid-Atlantic and the Northeast, Wed, Dec 16.

– Heavy snow across portions of the Great Lakes, the Mid-Atlantic, the Northeast, and the Central Appalachians, Wed-Thu, Dec 16-Dec 17.

– High winds across portions of mainland Alaska, Mon-Tue, Dec 14-Dec 15.

– Much below normal temperatures across portions of mainland Alaska, Wed-Fri, Dec 16-Dec 18.

Detailed Summary:

Throughout the medium range period (Monday, Dec 14 – Friday, Dec 18), a flurry of activity is forecast for both sides of the continental United States. On Tuesday, a low pressure/frontal system will propagate onshore from the northeast Pacific. The system itself, as well as subsequent upper level disturbances, will support a virtually continuous influx of moisture and precipitation hazards extending from Northern California through the Pacific Northwest throughout the period. Along the coastline and at lower elevations heavy rain will be the main threat, whereas heavy snow will be the primary concern at higher elevations along the Coastal Ranges and the Oregon and Washington Cascades. Since yesterday the models have trended toward lower and more uncertain precipitation totals in the Sierra Nevada, so it will not be included in the hazard area at this time. As this system moves along its eastward track it is expected to bring heavy snowfall to the Northern Great Basin, Northern Rockies, and potentially the Wind River Range/Tetons, Tuesday through Friday. In the neighboring Northern Great Plains, a series of warm fronts are expected to pass through the region throughout the medium range. This will help facilitate above normal, though non-hazardous, temperatures extending from Nebraska to the Canadian border Thursday and Friday.

Looking to the east, a low pressure system and its associated cold front will quickly pass through the Mid-Atlantic and Southeastern seaboards on Monday. While rain will accompany this system, the heaviest of which will be along the Virginia/North Carolina border, it is not expected to be hazardous. Later in the period, multiple surface lows spread throughout the Ohio River Valley and Southeast will combine late Wednesday and deepen, developing into the second nor’easter of the season. Friday’s model guidance has pointed towards a shift in the low track past Wednesday evening from a northeastward to eastward trajectory. This change in the low track could shift the forecasted snowfall and mixed eastward trajectory persists a majority of the hazardous weather over the region will likely occur on Thursday, with snowfall lingering in Northern New England into Friday. As this event is still evolving with time, it will continue to be monitored in the coming days.

In Alaska, a persistently strong high pressure system in the Arctic Ocean opposed by strong low pressure systems in the Gulf of Alaska will set up a strong pressure gradient over the mainland. This enhanced pressure gradient will produce high winds from Monday into Tuesday, which could cause blowing snow and the lowering of visibility. The main areas impacted will be the Far North and the Interior from the Seward and Lisburne Peninsulas in the west through Fairbanks in the east. Wednesday through Friday temperatures are expected to drop much below normal in the eastern Interior, reaching as low as -40F. Prolonged exposure to these temperatures can pose a risk to health and safety.

Toward the end of the period there is a wide spread in model solutions concerning a low pressure system that could impact the Alaska Panhandle and southern Mainland. While this system has the potential to produce heavy precipitation and high winds, no hazards will be issued at this time due to the uncertainty associated with its location and intensity.

(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.

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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