Written by Sig Silber

HEADLINES (Updated 6:14 PM EST) –

– Merry Christmas!!

– Heavy rain and flooding likely across portions of New England through Saturday morning

– Intense lake effect snow downwind from the Lower Great Lakes through early Sunday

– Heavy snow over parts of the Cascades, Sierra Nevada, and the northern Rockies

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.

Please share this article – Go to the very top of the page, right-hand side for social media buttons. Also, feel free to send this email to anyone you feel will benefit from it.

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 – 236 PM EST Fri Dec 25 2020

Valid 00Z Sat Dec 26 2020 – 00Z Mon Dec 28 2020

…Heavy rain and flooding likely across portions of New England through Saturday morning…

…Intense lake effect snow downwind from the Lower Great Lakes through early Sunday…

…Heavy snow over parts of the Cascades, Sierra Nevada, and the northern Rockies…

This Christmas has brought plenty of frightful weather across New England, where heavy rain and gusty winds are expected to continue into the overnight hours. The combination of heavy rain and warmer than average temperatures has also led to a rapid melting of the previously fresh snowpack. As a result, flooding is likely across parts of northern New England through Saturday as rivers and streams fill with rain and melting snow. WPC has placed a Moderate Risk of Excessive Rainfall that extends from southeast Vermont through central Maine. Flood Watches and Warnings have also been issued. The strong cold front responsible for the unpleasant weather will dash eastward by Saturday, leaving any leftover precipitation to fall as light snow.

However, snow will not be as light downwind of Lake Erie and Lake Ontario through Sunday morning. Strong westerly winds, warm lake temperatures, and cold air temperatures aloft will make for a favorable environment for heavy lake effect snow. In the typical snow belts southeast of Lake Erie and east of Lake Ontario, upwards of 1 to 2 feet of snow could fall. Lighter amounts will also be possible across northern Michigan and the Upper Peninsula of Michigan.

Across the western United States, a low pressure system is forecast to enter the Pacific Northwest tonight and bring wintry weather of its own. Heavy snow over 6 inches will be possible across the northern Sierra Nevada, much of the Cascades, and portions of the northern Rockies as well. Rain will be likely along the West Coast, with light rain as far south as central California Saturday morning. As the system exits into the Plains during the day on Sunday, light snow is expected across the northern tier and eventually into the Upper Great Lakes by late Sunday.

Temperatures are expected to remain quite cold on Saturday across the Southeast. In fact, Hard Freeze and Freeze Warnings have been issued for northern and Central Florida. Meanwhile, temperatures 10 to 15 degrees above average will be found across the central U.S. to start the weekend, before extending into the Ohio and Tennessee valleys on Sunday.

Merry Christmas and Happy Holidays from WPC!

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 28 2020 – Friday January 01 2021

Hazards:

– Heavy precipitation across portions of California, Mon-Tue, Dec 28-Dec 29.

– Heavy precipitation across portions of the Central Rockies, Mon, Dec 28.

– Heavy precipitation across portions of the Central Plains, the Middle Mississippi Valley and the Great Lakes, Tue-Wed, Dec 29-Dec 30.

– Heavy precipitation across portions of the Southern Appalachians, Wed-Thu, Dec 30-Dec 31.

– Heavy precipitation across portions of the Northeast, Fri, Jan 1.

– Heavy rain across portions of California and the Pacific Northwest, Wed-Thu, Dec 30-Dec 31.

– Heavy rain across portions of the Central/Southern Plains and the Middle/Lower Mississippi Valley, Tue, Dec 29.

– Heavy rain across portions of the Middle/Lower Mississippi Valley, the Tennessee/Ohio Valley, the Southeast and the Southern Plains, Wed, Dec 30.

– Heavy rain across portions of the Northeast, Mid-Atlantic and the Southeast, Thu, Dec 31.

– Heavy snow across portions of the Pacific Northwest, Wed, Dec 30.

– Heavy snow across portions of the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Wed-Thu, Dec 30-Dec 31.

– Heavy snow across portions of the Northern/Central Plains, the Upper Mississippi Valley and the Great Lakes, Tue-Wed, Dec 29-Dec 30.

– Heavy snow across portions of the Northeast, Mon, Dec 28.

– Flooding possible across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Ohio Valley.

– Flooding occurring or imminent across portions of the Pacific Northwest.

– Heavy precipitation across portions of mainland Alaska, Mon-Tue, Dec 28-Dec 29.

Detailed Summary:

Much of the CONUS will experience hazardous weather during the medium range period (Monday, December 28th – Friday, January 1st). A potent area of surface low pressure is forecast to produce heavy snowfall over interior portions of the Northeast on Monday, particularly over the Adirondacks. Heavy snow also remains a threat downwind of lake Ontario. An upper-level low will enter the West coast on Monday, bringing with it the likelihood for heavy snow to the Sierra and heavy rain to the surrounding low elevations.

The aforementioned system is forecast to restrengthen and generate a low pressure system over the Southern Plains on Tuesday. This system will go on to produce a swath of heavy snowfall from Nebraska to Michigan’s Upper Peninsula on Tuesday and Wednesday. Heavy precipitation is likely to stretch from the Central Plains to the Great Lakes on Tuesday into Wednesday, while heavy rain is expected across the Central/Southern Plains and into the Middle/Lower Mississippi Valley on Tuesday. The focus for heavy rain is expected to shift eastward into the Lower/Middle Mississippi/Tennessee Valleys and Southeast on Wednesday. As the low pressure system deepens and moves into the Midwest and eastern U.S. on Thursday (New Years Eve), it will generate heavy rainfall across the eastern seaboard from the Carolinas up to New England. Heavy precipitation is possible over parts of southern Maine and northern Vermont/New Hampshire as the system moves off into the Canadian maritime on Friday (New Years Day). We’re monitoring the possibility of a heavy rain event occurring over the coastal California/Oregon border between next Wednesday and Thursday as a slow moving low pressure system approaches from the Pacific. This is also an area that is currently experiencing a severe drought, so additional hazards may occur.

Meanwhile in Alaska, while the Aleutians and mainland west coast may experience some high winds on Saturday and Sunday as a very deep area of low pressure moves itself into the Bering Sea. Heavy precipitation is also a threat over the eastern portion of the Kenai Peninsula on Monday and Tuesday as moisture overspreads a surface front associated with the Bering Sea low.

(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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