Written by Sig Silber

Updated at 6:45 pm EDT Sunday May 17, 2020 – “…Tropical Storm Arthur is forecast to move close to the North Carolina coast overnight into Monday……Heavy rainfall and flash flooding expected with thunderstorms over portions of the Midwest through tonight and the Ohio Valley Monday……Rain and higher elevation snow forecast to continue across portions of the West……Fire weather danger will be widespread across portions of the Central Great Basin, Southwest, and Four Corners region…”

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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CONUS Focal Points

Short Range Focal Points

Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Sun May 17 2020 Valid 00Z Mon May 18 2020 – 00Z Wed May 20 2020

…Tropical Storm Arthur is forecast to move close to the North Carolina coast overnight into Monday…

…Heavy rainfall and flash flooding expected with thunderstorms over portions of the Midwest through tonight and the Ohio Valley Monday…

…Rain and higher elevation snow forecast to continue across portions of the West…

…Fire weather danger will be widespread across portions of the Central Great Basin, Southwest, and Four Corners region…

Tropical Storm Arthur is expected to move northward overnight and approach the Outer Banks of North Carolina. Tropical Storm Warnings are in effect for portions of the North Carolina coast, where tropical-storm-force winds are expected along with locally heavy rain. Dangerous coastal surf and rip currents are foreca st to spread northward from the Southeast into the Mid-Atlantic over the next couple of days. Please see the National Hurricane Center for more information on Arthur.

A surface low pressure system is forecast to slowly meander over the Ohio Valley over the next couple of days, and rain and thunderstorms are likely in its vicinity and southward along its associated warm front. Today into tonight, a Moderate Risk of flash flooding and a Slight Risk of severe weather are in place for much of Illinois and western parts of Indiana, with some severe and flash flooding risk stretching farther south as well. Then on Monday, a Moderate Risk of flash flooding is outlined across portions of the Ohio Valley, with a Slight Risk of excessive rainfall farther north over the Upper Great Lakes and southward toward the Southern Appalachians. Flash Flood and Flood Watches are also in effect, and strong to severe thunderstorms are also possible.

A frontal system will continue to move slowly eastward across the Intermountain West over the next couple of days ahead of a deep upper-level low making its way into the West Coast. Pacific moisture should continue to cause precipitation in the Pacific Northwest, California, and increase over the Great Basin Monday and Tuesday. While most precipitation will fall as rain, the Sierra Nevada could receive several inches of snow, and some Winter Storm Warnings are in effect.

In between the upper-level low in the West and the systems in the eastern half of the country, upper-level ridging is expected across the Great Basin into the Rockies and Plains. This will lead to temperatures that are above average by 10 to 20 degrees in those areas underneath the ridge. The dry, hot conditions could also cause fire danger, and the Storm Prediction Center has Elevated to Critical Risks for fire weather in place today through Tuesday for portions of the Southwest, Central Great Basin, and Four Corners. Red Flag Warnings are also in effect.

Click here for the latest complete NWS/WPC Short Range Discussion. (Sometimes we provide part of or even the full discussion above and you can tell because it goes beyond the bullet points. We do that when we think the bullet points do not provide enough information. But the link just provided always takes you to the full discussion with updates twice a day and sometimes we are a bit late updating the bullet points so that link will get you there. You can tell if we are late by the time of the stamped update. This time of the year, NOAA does the updates at around 3 a.m. and 3 p.m. EST. We try to do the updates in our article as close to that as possible but it is not always possible.)

There is a longer discussion of TS Arthur later in this report.

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.

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

Water Vapor.

This view of the past 24 hours provides a lot of insight as to what is happening.

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Day 3 – 7 Hazards

– Heavy precipitation across portions of California, Mon, May 18.

– Heavy rain across portions of the Northern Rockies, and the Northern Great Basin, Mon-Wed, May 18-May 20.

– Heavy rain across portions of the Northeast, the Central Appalachians, and the Mid-Atlantic, Mon-Wed, May 18-May 20.

– Flooding possible across portions of the Southern Plains, the Northern Rockies, the Middle Mississippi Valley, the Northern Great Basin, the Upper Mississippi Valley, and the Great Lakes. – Flooding occurring or imminent across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, and the Northern Plains.

– Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, and the Southern Plains.

– Much above normal temperatures across portions of the Northern/Central Plains, the Rockies, and the Upper Mississippi Valley, Mon-Thu, May 18-May 21.

– Enhanced wildfire risk across portions of the the Southern Rockies, the Central Rockies, the Central Great Basin, and the Southwest, Mon-Tue, May 18-May 19.

– Heavy precipitation across portions of mainland Alaska, Tue, May 19 and Thu, May 21.

Detailed Summary:

A highly amplified synoptic pattern will be the theme during the medium range period (Monday 5/18 to Friday 5/22). Models are in excellent agreement that a relatively flat upper-level pattern across the U.S. during the weekend will dramatically amplify into an omega block pattern, with a pronounced ridge sandwiched in between two major cut-off lows impacting both the West Coast and East Coast. Models dig down an upper trough quickly and aggressively from the Great Lakes into the eastern U.S. The current assessment of the situation calls for heavy rain to occur from the interior Northeast and Mid-Atlantic into the Central Appalachians next Monday through Wednesday.

Prior to the formation of this anomalous upper low over the East Coast, a threat of heavy rain is expected to impact areas from the lower Great Lakes eastward across the central Appalachians into parts of New England ahead of a pair of well-developed frontal boundaries and a low pressure system. This will be in stark contrast with a pronounced ridge of high pressure forecast to develop over the Great Plains. This ridge will ensure a significant warming trend across the northern and central Plains for early to middle of next week with afternoon temperatures likely reaching well up into the 80s to possibly the lower 90s.

Models continue to indicate the formation of a low pressure system fairly near the east coast of Florida this weekend. The National Hurricane Center continues to monitor this area for the potential of subtropical cyclogenesis. Impacts associated with this system are expected to remain largely offshore. However, with the major shift toward a major closed low developing over the eastern U.S., there is a possibility for the offshore subtropical system to mutually interact with the deep upper low over the East Coast and thus spreading moisture toward the eastern U.S.

Over the West Coast, a deepening upper-level trough is forecast to produce heavy rain across lower elevation portions of northern/central California on Monday. Meanwhile, heavy wet snow is expected for the higher elevations of the central Sierra Nevada next Monday into Tuesday as the upper trough digs further into California.

Over the Pacific Northwest, a frontal system moving onshore is expected to arrive, bringing localized areas of heavy rainfall to the Northern Great Basin/Rockies Monday through Wednesday. By Tuesday and Wednesday, the threat of heavy rain is forecast to spread from northern Idaho into western Montana ahead of a low pressure system. By Thursday, the heavy rain threat should linger across central Montana as the low pressure system begins to interact with a cold front arriving from western Canada. Wet snow can also be expected over the highest elevations in these areas.

Over Alaska, a pair of low pressure systems moving across the southern portion of the state could result in heavy precipitation along the southern coastal areas later on Monday into Tuesday as well as Wednesday into Thursday, respectively. Above normal temperatures are forecast to continue over the western and much of the southern portions of the state, in contrast with colder than normal temperatures over the north and northeast portions of the state.

(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. 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.

There is not much snow left.

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Tropical Events

This is now beyond the time of the year we pay special attention to Tropical Events other than the Western Pacific.

So 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.

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

Updates on individual named storms can be obtained here.

And the Western Pacific

Week 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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