Written by Sig Silber

HEADLINES (Updated 7:58 PM EST) –

– Higher elevation snow and a Slight Risk of excessive rainfall over parts of the Northwest

– Rain for parts of the Southeast and Southern Mid-Atlantic while a couple of rounds of light mixed precipitation or snow affect the Midwest to Northeast

– Heavy snow and rain over wide areas of US leading up to Christmas

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 – 332 PM EST Sun Dec 20 2020

Valid 00Z Mon Dec 21 2020 – 00Z Wed Dec 23 2020

…Higher elevation snow and a Slight Risk of excessive rainfall over parts of the Northwest…

…Rain for parts of the Southeast and Southern Mid-Atlantic while a couple of rounds of light mixed precipitation or snow affect the Midwest to Northeast…

Onshore-flow streams Pacific moisture into the Northwest that will slowly weaken after the next front comes onshore on Monday evening. The WPC has issued a Slight Risk of excessive rainfall over parts of the Pacific Northwest through Monday. The heavy rain associated with the system may produce scattered flooding areas where urban areas, roads, and small streams will be the most vulnerable. The heavy rain may also produce landslides and debris flows. Despite relatively high snow levels, snow will develop in higher elevations of the Northwest. The Washington Cascades can expect an additional 1 to 2 feet of snow. At the same time, the Northern Rockies, Sawtooth Mountains/Bitterroots, and Wind River Mountains/Tetons could see 6 to 12 inches of snow with locally higher amounts through Tuesday morning. Snow levels will lower by Monday night into Tuesday as an upper-level trough and cold front move in. Farther south, an Elevated Risk of fire weather is in place for Southern California through Monday morning, where low relative humidity exists.

A developing area of low pressure off the Southeast Coast will help produce showers and a few thunderstorms over parts of the Southeast and Southern Mid-Atlantic Coast through Monday. Farther north, weak upper-level energy will help create rain and snow across parts of the Lower Great Lakes and the Northeast, with the snow generally totaling an inch or so. In addition, an area of low pressure over the Northern Plains will move eastward to the Mid-Atlantic, and the associated front will dissipate by Tuesday morning. The system will produce rain and snow over parts of the Northern Plains that will move into the Great Lakes/Ohio Valley by Monday afternoon. Overnight Monday, the system will produce light snow over parts of Eastern Ohio Valley/Central Appalachians and Lower Great Lakes that will slowly taper off on Tuesday. Elsewhere, temperatures will be 10 to 20 degrees above average over parts of the Northern High Plains into parts of the Upper Midwest.

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 21 2020 – Friday December 25 2020

Hazards:

– Heavy precipitation across portions of the Cascades, Mon, Dec 21.

– Heavy precipitation across portions of northwestern Washington, Mon-Tue, Dec 21-Dec 22 and Fri, Dec 25.

– Heavy precipitation across portions of the central Appalachians into the interior Northeast, Thu-Fri, Dec 24-Dec 25.

– Heavy rain possible across portions of the interior Southeast into the southern Appalachians, Wed-Thu, Dec 23-Dec 24.

– Heavy rain possible across portions of the Mid-Atlantic into New England, Wed-Fri, Dec 23-Dec 25.

– Heavy rain possible across portions of the North Carolina coast, Thu-Fri, Dec 24-Dec 25.

– Heavy snow across portions of the northern Rockies, Mon-Tue, Dec 21-Dec 22.

– Heavy snow possible over northwestern Wyoming, Tue, Dec 22.

– Flooding possible across portions of western Washington.

– Flooding likely across portions of the western Washington.

– High winds across portions of southeastern Wyoming, Mon, 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, Mon-Tue,

Dec 21-Dec 22.

Detailed Summary:

The active synoptic pattern over the northeastern Pacific will continue into the medium range period (Monday, Dec 20 – Friday, Dec 25) as additional moisture-laden and energetic frontal systems are forecast to impact the Pacific Northwest with heavy precipitation along the Cascades and northwestern Washington early next week. Further inland, heavy snow is expected to continue across portions of the northern Rockies in Idaho and western Montana on Monday before tapering off later on Tuesday as a developing low pressure system exits into the northern Plains. Portions of northwestern Wyoming could see heavy snow as well on Tuesday. Meanwhile, strong Chinook winds over southeastern Wyoming should gradually diminish on Monday as the previous low pressure system moves away into the upper Midwest. This will be quickly followed by the aforementioned low pressure system which should deliver a period of wintry precipitation across the upper Midwest to the Great Lakes Wednesday to Thursday. In the wake of this low pressure system, the Pacific Northwest will likely catch a break from the active weather as a strong ridge of high pressure aloft is forecast to build near the West Coast by the middle of next week. It appears that moisture from the next Pacific system will still be off the coast of the Pacific Northwest on Christmas Eve. However, chance of precipitation will likely increase on Christmas Day and it may become heavy over northwestern Washington.

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 for the interior Southeast, possibly up the Appalachians by later on Wednesday into Thursday. Models have been showing an increasingly amplified synoptic pattern moving into the East Coast during the latter part of next week. There is a possibility of widespread strong wind gusts together with wild swings in temperatures up and down the East Coast on Christmas Eve to Christmas Day if the upper trough and the associated front amplify like it is depicted by the GFS and the latest ECMWF. Heavy rain is also possible preceding the strong cold front, and could rapidly change over to snow behind the front. Any heavy rain falling over the interior Northeast on top of the recent snow pack would be a bad recipe for snow melt, which could result in flash flooding.

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 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 into 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 will probably 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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