


Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
154 FOUS30 KWBC 181953 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 353 PM EDT Fri Jul 18 2025 Day 1 Valid 16Z Fri Jul 18 2025 - 12Z Sat Jul 19 2025 ...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL FOR THE NORTHERN SHENANDOAH VALLEY OF NORTHERN VIRGINIA INTO SOUTHEAST VIRGINIA... 20Z update... The MDT risk was expanded to include more of southeast VA. Instability and moisture continues to build along a stationary backdoor front over this region. Convection currently over central and southwest VA should stream into this corridor later this afternoon and evening. Wet antecedent conditions have left this area susceptible to additional flash flooding...and the high PWs and nearly stationary front supports some instances of 2"+ per hour rainfall...likely enough to result in scattered to numerous instances of flash flooding. See MPD 746 for additional info. Recent observational trends and the presence of a well defined MCV warranted the expansion of both the Marginal and Slight risk areas across portions of southeast CA and southern NV. The Slight risk was removed across the central Gulf Coast. Still plenty of moisture around, but convection should continue to lack organization and coverage. Thus generally expect any additional flash flooding to stay localized in nature over these areas. Chenard ...Previous Discussion... ...Mid-Atlantic... The biggest changes for today`s outlook were made across the Mid- Atlantic. Abundant moisture that has been in place across much of the Mid-Atlantic for at least the past week will only build today as a steady supply of deep tropical moisture from the Gulf pushes northeastward across the South and into the Mid-Atlantic. This moisture will contain ample instability for storms to draw on as MUCAPE values exceed 3,000 J/kg across much of VA and points south. The primary forcing will be a back door front of sorts, though it`s more of a dry line. The front will gradually sag southward, making the most southward progress down the coast. Thus, the front will become more northwest-to-southeast oriented with time. The front acting as a focal point for lift will allow widespread shower and thunderstorm activity to develop across West Virginia as early as mid-to-late-morning. As these storms progress eastward, they will encounter areas that have been hard-hit with heavy rain and therefore have swollen streams and creeks and saturated soils, such as in the northern Shenandoah Valley. After the first round of storms moves through around midday or so, additional storms will quickly develop behind it over the northern Shenandoah Valley and then they too will push southeastward, gradually organizing into clusters and lines of storms. The likelihood for the northern Shenandoah Valley to act as a focus for the storms to initially develop and organize has increased markedly with the latest guidance. HREF probabilities of exceeding 3 and 6 hour FFG values are over 70% through the late afternoon. This is in significant part due to the aforementioned saturated soils across the area. Further, neighborhood probabilities of exceeding 3 inches of rainfall are over 70% for the afternoon period, and over 25% for exceeding 5 inches of rain. Much of that rain will fall with the heaviest storms, as local rainfall rates may exceed 3 inches per hour at times. For these reasons, in coordination with LWX/Sterling, VA forecast office, a Moderate Risk upgrade was introduced with this update for the I-81 corridor in the northern Shenandoah Valley, which includes the westernmost portion of I-66. Elsewhere, the Slight Risk was expanded north and west with the latest guidance suggesting morning convection will impact far northern West Virginia, and likely train as it moves into far western Maryland. Recent rainfall and the very flashy nature of the streams and creeks in that area also support the Slight Risk upgrade in these areas. ...Gulf Coast... 16Z update... Convection circulating along the coastline and points inland will continue to produce a few inches over saturated areas today. The threat for flash flooding will remain elevated, therefore no adjustments were made to the Slight or Marginal Risk areas. Campbell The tropical disturbance centered near New Orleans and Lake Pontchartrain at the time of this writing continues to produce very limited shower and thunderstorm activity well to its west over southwestern Louisiana. Over the next few predawn hours, thunderstorm activity is likely to markedly increase both east and west of the center of circulation. To the west, the northerly flow west of the center will collide with the broader southerly flow over much of the rest of the Gulf, likely leading to a localized convergence zone near the southwestern Louisiana coast. This will result in a localized maximum of rainfall in that area. Meanwhile to the center`s east, the complimentary southerly flow over the Gulf and east of the center will support strong advection of deep tropical moisture. North-south oriented lines of cellular convection will developing also likely near the coast, where frictional convergence increases. These lines are likely to remain nearly stationary since the center of circulation will be moving nearly due north, so the forcing from the low center will remain steady state. For these reasons, the Slight Risk in the ERO was maintained largely unchanged, though there will likely be a minimum of thunderstorm activity in between these two maxima in eastern Louisiana. Despite this minimum, the abundance of tropical moisture present will still support isolated to widely scattered convection near the center which will be very capable of embedded heavy rainfall. ...Midwest... 16Z update... The setup still favors backbuilding and training of thunderstorms this afternoon and evening over much of the region. The Slight Risk still covers the areas with elevated threat for excessive rainfall and local flooding concerns. Campbell The nose of a potent southwesterly LLJ will intrude into the Iowa/Minnesota/Wisconsin area through the day today. As an upper level shortwave digs south out of the jet over northern Minnesota, the front at the nose of the LLJ will act as a focal point for strong thunderstorms. PWATs will increase above 1.75 inches over the area, which will supply plentiful fuel for the thunderstorms to produce cells of heavier rainfall as they track southeastward along the front. The LLJ will support backbuilding and training storms as the moisture and instability supply with the LLJ remains in place to allow for additional thunderstorm development behind any initial line of storms. As the storms move into the instability, expect any initial clusters to organize into one or two lines of storms as they press into Iowa. Due to the potential for heavy rain and recent heavy rainfall having partially saturated the soils in the area, the Slight Risk remains in place across the region, particularly for the localized areas where storms train and backbuild. The rather fast movement of the storms should somewhat limit the flash flooding potential, so the area remains a lower end Slight. ...Southwestern New Mexico... 16Z update... no changes made. Campbell A tongue of higher moisture across southwestern New Mexico today will act as a focus for widespread shower and thunderstorm activity this afternoon with maximum daytime heating. The showers and storms will be capable of locally heavy rainfall, though PWATs only around 1.25 inches may limit the overall coverage of any heavier convection. The storms may organize around any local terrain features. Local burn scars and shallow soils will both contribute to potential flash flooding as the rainfall quickly flows into the local streams and rivers. The Slight was left unchanged from inherited as guidance remains in good agreement on the location of the highest flash flooding potential. ...Eastern Nevada... 16Z update... The environment remains conducive for isolated areas of heavy rainfall and possible flash flooding. No changes were made. Campbell The Slight Risk area across eastern Nevada and a sliver of Utah also remains unchanged with this update. A slow, northward moving upper level low will help concentrate the available atmospheric moisture in the area to allow any storms that form with afternoon heating to persist and perhaps organize into a slow-moving line of storms by the evening hours. The Slight Risk area was unchanged from the previous update in this area. Wegman Day 2 Valid 12Z Sat Jul 19 2025 - 12Z Sun Jul 20 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDWEST INTO THE TENNESSEE VALLEY AND THE SOUTHERN MID-ATLANTIC... 21Z update... Campbell Ample tropical moisture, at least in part associated with the plume of moisture associated with the low over Louisiana will stream northeastward on a continuous low level jet. As that moisture runs into a stationary front set up over the Midwest, it will be lifted, resulting in numerous showers and thunderstorms all across the region. The guidance is in poor agreement as to how those thunderstorms will organize. What appears most probable is the cluster of thunderstorms from the upper Midwest on Day 1/Friday will continue southeastward along the front, able to easily sustain itself due to the abundant tropical moisture in place across much of the eastern half of the US. With daytime heating, clusters of showers and thunderstorms will develop ahead of this aforementioned line. Cell mergers and the eventual congealing of the storms with the line will allow quite a few areas across the Midwest to have multiple rounds of storms to impact the area. This will likely result in widely scattered to scattered instances of flash flooding. Areas hard hit with heavy rainfall in previous days would be particularly vulnerable to additional flash flooding should multiple rounds of storms move over those communities. Wegman Day 3 Valid 12Z Sun Jul 20 2025 - 12Z Mon Jul 21 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MIDWEST AND NORTHERN PLAINS... ...Midwest and the Ohio/Tennessee Valleys... 21Z update... The latest guidance suggested a small uptick in QPF over Iowa so made a small westward expansion of the Slight in that vicinity. Also the southward trend previously noted (below) also warranted a minor southward expansion of the Slight Risk into far northern Alabama and Georgia. Campbell A complex setup looks to unfold across this region on Sunday. A line of storms will move southeastward from the Mississippi River Valley across the Ohio Valley. With ample daytime heating and a stationary front still in place. Widespread thunderstorms will develop along the frontal interface. The storms will interact with each other, likely congealing into clusters as the line absorbs the storms from northwest to southeast. Behind this line however, additional storms are likely to develop overnight Sunday night, especially for western areas in Iowa and Illinois. The slow moving nature of the storms at the nose of the jet will increase the flash flooding threat in that region as well. Further, all of the Slight Risk area will have been through storms from the Day 2/Saturday period, so soils are likely to be more responsive to flash flooding should storms occur in these same areas again on Sunday. There is some uncertainty as to where the storms will align, which will depend on frontal position. Much of the guidance has trended a bit southwestward, so the Slight was trimmed out of northern Indiana and Illinois with this update in favor of the central portions of those same states. Into Kentucky and the western Virginias, terrain and recent heavy rainfall increase the flash flooding threat further in these areas, where a higher end Slight remains in effect. ...Northern Plains... 21Z update... No significant differences noted in the latest guidance that would suggest an adjustment to the Slight or Marginal Risk ares over the Dakotas. Campbell Much of North Dakota will be at the nose of a potent low level jet across the area. A subtle shortwave in the upper level jet may be all it takes to initiate a line of storms across the region, especially Sunday night, though there may be two separate rounds: one in the morning and a second Sunday night. There is considerable uncertainty both with storm intensity and receptivity of the ground to the heavy rainfall. Due to this uncertainty, the Slight Risk area was left unchanged with this update, but is considered a lower end Slight. Wegman Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt