Written by Sig Silber

HEADLINES (Updated 5:24 PM EST) –

– Record breaking December winter storm heads out to sea this evening, cold and dry conditions to linger over the Northeast to end the week

– Light snow expected across the northern and central Rockies, showers and thunderstorms possible in the South Central U.S. on Saturday

– Coastal/valley rain and mountain snow continues across the Pacific Northwest

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 – 258 PM EST Thu Dec 17 2020

Valid 00Z Fri Dec 18 2020 – 00Z Sun Dec 20 2020

…Record breaking December winter storm heads out to sea this evening, cold and dry conditions to linger over the Northeast to end the week…

…Light snow expected across the northern and central Rockies, showers and thunderstorms possible in the South Central U.S. on Saturday…

…Coastal/valley rain and mountain snow continues across the Pacific Northwest…

Snow falling along the New England coast this afternoon will come to an end later tonight as last night’s Nor’easter heads out to sea. Astonishing snow totals were observed across the interior Northeast with some locations seeing more than 40 inches of snow. As the storm exits east a dome of Canadian high pressure builds in, leading to a dry and cold stretch of weather this evening and through Friday. Lows will range from the 10s to 20s from the Northeast on south into the northern Mid-Atlantic. This will lead to re-freezes and patchy areas of black ice on untreated roads. High temps may struggle to get above freezing on Friday and Saturday in locations with deep snow pack.

As the weather quiets down up and down the East Coast, the more active weather pattern sets up across the western half of the country. An upper level trough swinging through the Great Basin is responsible for snow falling across the northern and central Rockies this evening. Over 6 inches of snow is likely in the higher elevation regions of the Intermountain West. Isolated travel disruptions can be expected in the typical slick spots, but overall nothing too uncommon for the region. By Friday morning, the storm system heads into the Plains with light snow expected in the central High Plains. The aforementioned upper trough reaches the Southern Plains on Saturday and is expected to develop a new wave of low pressure in the western Gulf of Mexico. Scattered showers and thunderstorms are likely to track through the South-Central region and into the Lower MS Valley Saturday afternoon. Meanwhile to the north, a cold front racing across the Upper Midwest looks to trigger snow showers across northern Minnesota, northern Wisconsin, and the upper peninsula of Michigan.

The Pacific Northwest has experienced several rounds of precipitation over the last week and this pattern should continue over the next couple of days. Precipitation across the region will back down to a degree overnight, but a new Pacific storm system arrives on Friday with coastal/lower elevation rain and heavy snow in the Cascades and Olympics. Another break in the action arrives on Saturday, but yet another storm system looks to slam into western Washington Saturday night. In total over the next couple days, anywhere from 1 to 2 inches of rainfall is possible in parts of western Washington and Oregon. The northern Cascades could accumulate up to 2 feet of snow through Saturday evening.

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 Sunday December 20 2020 – Thursday December 24 2020

Hazards:

– Heavy precipitation across portions of the Pacific Northwest, Sun-Mon, Dec 20-Dec 21.

– Heavy snow across portions of central Idaho into northeastern Oregon, Sun, Dec 20.

– Heavy snow across portions of the northern Rockies, Sun-Tue, Dec 20-Dec 22.

– Flooding possible across portions of western Washington.

– Flooding likely across portions of northwestern Washington.

– High winds across portions of western Montana, Sun, Dec 20.

– High winds across portions of southeastern Wyoming, Sun-Mon, Dec 20-Dec 21.

– Heavy precipitation across the Alaska Peninsula into southern Alaska, Mon-Wed, Dec 21-Dec 23.

– Heavy precipitation across portions of the Alaska Panhandle into southern Alaska, Wed, Dec 23.

– High winds across the Alaska Peninsula into southern Alaska, Mon-Tue, Dec 21-Dec 22.

– Much below normal temperatures across much of the lower elevations of eastern Alaska, Sun-Tue, Dec 20-Dec 22.

Detailed Summary:

The active onshore flow pattern across the Pacific Northwest will continue into the medium range period (Sunday, Dec 19 – Thursday, Dec 24) as additional moisture-laden and energetic frontal systems are forecast to impact the area with heavy rain for the lower elevations and heavy snow from the Coastal Ranges to the Oregon and Washington Cascades. Further inland, heavy snow is expected across the northern Rockies in Idaho, northeastern Oregon, and western Montana late this weekend into Monday, before tapering off later on Tuesday as a developing low pressure system exits into the northern Plains. In the wake of the system, winds across parts of the eastern slopes of the northern Rockies could be impacted by very strong Chinook winds on Sunday and into Monday. By the middle of next week, it appears that the Pacific Northwest will catch a break from the active weather as a strong ridge of high pressure aloft is forecast to build near the West Coast.

Along the Gulf Coast, moisture from the Gulf of Mexico is forecast to return by the middle of next week. A cold front approaching from the Great Plains together with a developing low pressure wave could increase the chance of heavy rainfall from portions of the Gulf Coast to the interior Southeast, possibly up the Appalachians by next Wednesday into Thursday. The uncertainty is currently too high to warrant a heavy rain area at this time.

Temperature-wise, the active zonal flow from the Pacific will result in above to well above normal temperatures across the northern tier states into the central Plains with temperatures ranging anywhere from 10 to 25 degrees above normal early in the medium range period. Though anomalous, these temperatures are not expected to be hazardous. As the aforementioned ridge of high pressure builds near the West Coast, colder air from central Canada will be encouraged to dip into the Plains by next Wednesday into Thursday, resulting in below normal temperatures to return.

Meanwhile, the active synoptic pattern over the northeastern Pacific will continue to direct large and energetic cyclones downstream toward Alaska during the medium range period. One such cyclone is forecast to bring widespread gale to storm force winds and heavy precipitation across the Aleutians on Sunday before spreading through the Alaska Panhandle on Monday. By Tuesday, much of the Alaska Peninsula into the southern portion of mainland will likely be engulfed with very gusty south to southeasterly winds along with heavy precipitation which should linger into Wednesday. In addition, some of the heavy precipitation is forecast to reach the Alaska Panhandle on Wednesday. There could be another cyclone approaching the Alaska Panhandle on Thursday but uncertainty remains high at this time. Farther inland across the lower elevations of eastern Alaska, much below average high and low temperatures are expected to continue into early next week, where temperatures are expected to reach as low as -35 to -40F. However, a general warm-up is forecast spread from southwest to northeast through Alaska from early to middle of next week.

(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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