Written by Sig Silber

Updated at 5:36 pm EDT Monday May 18, 2020 – “…A slow-moving system is likely to produce very heavy rains and flash flooding from the Ohio Valley to western Virginia and the Carolinas……Tropical Storm Arthur to produce dangerous surf conditions and rip currents along the Mid-Atlantic coast……Flooding possible across portions of California, the Pacific Northwest and the northern Rockies……Critical fire weather conditions to continue across portions of the 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 404 PM EDT Mon May 18 2020 Valid 00Z Tue May 19 2020 – 00Z Thu May 21 2020

…A slow-moving system is likely to produce very heavy rains and flash flooding from the Ohio Valley to western Virginia and the Carolinas…

…Tropical Storm Arthur to produce dangerous surf conditions and rip currents along the Mid-Atlantic coast…

…Flooding possible across portions of California, the Pacific Northwest and the northern Rockies…

…Critical fire weather conditions to continue across portions of the Southwest and Four Corners Region…

A slow-moving system will continue to produce heavy rains across portions of the Ohio Valley on Monday before shifting into the southern Appalachians, Carolinas, and western Virginia on Tuesday and Wednesday.  This system is expected to produce several inches of rain, with flash flooding likely, especially across portions of Indiana, Kentucky and Ohio on Monday and then across parts of the western Carolinas and Virginia Tuesday and Wednesday.  In addition to heavy rains, there is also the potential for strong to severe thunderstorms to develop, especially across portions of eastern Kentucky and central Ohio Monday afternoon and evening.

Farther east, Tropical Storm Arthur will continue to track east away from the North Carolina Outer Banks.  However, dangerous coastal surf conditions and rip currents are forecast to spread north along the Mid-Atlantic coast and persist during the next couple of days.

Meanwhile, an upper level low moving east from the eastern Pacific is expected to produce widespread precipitation across the western U.S.  This includes higher elevation snow, with several inches forecast to accumulate across the higher peaks of the Sierra.  Significant rainfall accumulations are forecast for portions of the Sierra foothills and the interior valleys of California — raising the potential for flash flooding across those areas.  Significant rains along with snowmelt will also raise flooding concerns across portions of the Northwest and northern Rockies.

Dry and windy conditions will prevail across the Southwest – promoting elevated to critical fire weather conditions across much of the Southwest through the Four Corners region on Tuesday.

More information on TS Arthur is provided later in the report.

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.)

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 rain across portions of the Plains and the Mississippi Valley, Thu-Mon, May 21-May 25. – Heavy rain across portions of the Southern Appalachians, the Mid-Atlantic, and the Central Appalachians, Thu, May 21.

– Flooding possible across portions of the Central/Southern Appalachians, the Northern Rockies, the Middle Mississippi Valley, the Mid-Atlantic, the Northern Great Basin, the Great Lakes, and the Ohio Valley.

– Flooding occurring or imminent across portions of the Mississippi Valley, the Great Lakes, and the Northern Plains.

– Flooding likely across portions of the Middle Mississippi Valley, the Northern Rockies, and the Northern Great Basin.

– Heavy precipitation across portions of mainland Alaska, Thu-Sat, May 21-May 23.

Detailed Summary:

The medium range period will begin on Thursday 5/21 with a cutoff upper-level low continuing to meander over the Tennessee and Ohio Valleys. Due to this low, heavy rainfall should persist into Thursday over portions of the Appalachians and Mid-Atlantic, with several inches of rainfall expected to accumulate from the short range period through Thursday night. The upper-level low is forecast to move eastward and offshore over the weekend.

The western half of the U.S. should see a general upper-level trough pattern through the weekend, with a couple rounds of shortwave energy enhancing the trough. Underneath, some precipitation is forecast to continue across the Northern Great Basin to Northern Rockies late in the week, and some snow is expected in higher elevations. But the broader concern is ahead of this trough. Moisture inflow could interact with a series of frontal boundaries traversing the Plains and Mississippi Valley through early next week, leading to the potential for heavy rain and thunderstorms in those regions. At this point, model guidance varies quite a bit on position and timing of heavy rainfall, and it seems some areas could see multiple rounds of rainfall. So the broad Heavy Rain hazard area may be refined spatially and temporally over the coming days as model guidance hopefully becomes more consistent and in better agreement. Severe weather is also a possibility, and its potential is being monitored by the Storm Prediction Center.

The trough in the West will lead to maximum temperatures of 10 to 15 degrees below normal over the Northwest through the end of the week, though minimum temperatures should not be considerably below average. Farther east, somewhat warmer than average temperatures are expected for parts of the Plains to Great Lakes region through early next week.

Over Alaska, there is a good signal for heavy precipitation through the end of the week for eastern portions of the Alaska and Kenai Peninsulas. Then, there is some potential for precipitation over the weekend and early next week for parts of the Panhandle, but model guidance has not settled on a consistent signal for precipitation there. Ice jam flooding will be a concern over the North Slope as rivers have not yet broken up, while minor snowmelt flooding is a possibility in central and southern parts of the mainland. No significant temperature anomalies are expected, but southern parts of the mainland will generally see below average high temperatures, with warmer than average temperatures in central and parts of the northern mainland.

(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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