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< Day 1 Outlook Day 3 Outlook >
 
WPC Day 2 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
 
Updated: 0757 UTC Tue Feb 27, 2024
Valid: 12 UTC Feb 28, 2024 - 12 UTC Feb 29, 2024
 
Day 2 Excessive Rainfall Forecast
 
Forecast Discussion
 
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
301 AM EST Tue Feb 27 2024
 
Day 2
Valid 12Z Wed Feb 28 2024 - 12Z Thu Feb 29 2024 

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF 
THE UPPER OHIO VALLEY THROUGH NEW ENGLAND, AS WELL AS THE COASTAL 
PACIFIC NORTHWEST...

...Mid-Atlantic and Northeast...

Progressive, but potent shortwave trough will eject east-northeast 
while evolving from a neutral to negative tilt as it crosses east 
of the Mississippi. A strong cold front will press east through 
the Ohio Valley into the Mid-Atlantic and Northeast by the second 
half of the forecast period. A line of organized showers and 
embedded thunderstorms will rumble eastward with locally heavy 
rainfall situated within the confines of the linear segment thanks 
to focused ascent along the cold front. Meridional flow ahead of 
the mean trough will pump deeper moisture poleward allowing for 
2-3 deviations above normal PWATs to be positioned across the 
Mid-Atlantic and Northeast with as much as 4 standard deviations 
forecast for portions of Northern New England. There are two main 
areas of concern for flash flooding potential, both of which are 
within the terrain and also have the added effect of snow melt 
with NOHRSC snow-water equivalent (SWE) estimates pinpointing some 
modest SWE available to couple with the heavier rainfall. The 
first area is within the central Appalachians across the high 
country of WV into Western MD where organized convection out of OH 
will likely propagate eastward with forcing maximized within the 
terrain encompassing Tucker/Grant/Randolph counties in WV, and 
Garrett county in MD. There's a very good signal for at least 1" 
of rainfall during Wednesday morning with locally as high as 2" 
within some hi-res deterministic. Given the current SWE available 
and expected heavy rainfall, some flood concerns will arise as 
regional streams and rivers could flood their banks in a few 
locations, especially within the rugged terrain situated in those 
aforementioned counties. There will be a transition back to snow 
after the cold front moves through the region and upslope flow 
takes over, so the threat is mainly in the first half of the 
forecast cycle, but the threat is certainly warranted. 

The second area of interest is across Upstate NY into New England 
where the same issues will be found as locally heavy rains mixed 
with the rapid snow melt could induce some flooding prospects 
where SWE is readily available and rainfall rates reaching up to 
0.5"/hr prior to the cold front passage. The the main concerns 
will be during the morning and early afternoon hours Wednesday 
before the cold front pushes through and the falling height 
pattern and 1000-500mb thicknesses crash rapidly post front with 
snow taking over shortly after. There's a bit less enthusiasm for 
the rainfall totals reaching above 1-1.25" on guidance currently, 
but the environment is ripe for some totals to reach within that 
1.5-2" range which would spell a better risk for flood potential 
given the components mentioned above. The Marginal Risk in place 
from the previous forecast was changed very little as the overall 
consensus of the pattern evolution and expected rainfall is fairly 
lock steady outside some shifts in the QPF maximums due to 
convective variability. 


...Pacific Northwest...

The next atmospheric river will take shape across the PAC 
Northwest with a minor to bordering moderate AR forecast expected 
as IVT values between 500-700 kg/ms are expected to advect into 
WA/OR by Wednesday morning, onward. This event will be 
characterized by longevity of moderate rainfall and less of 
short-term magnitude of rainfall as probabilistic fields are all 
fairly tame for the prospects of any hourly rates reaching the 1" 
mark. Most of the heaviest rain will settle between 0.5-0.75"/hr 
with the heaviest rainfall positioned over northwest OR where both 
the GEFS/ECENS means both pinpoint the heaviest precip totals 
within the period. Expect 2-4" to be fairly common within the 
coastal plain extending from the Olympic Peninsula down through 
southwest OR as we move into Thursday morning. When you add that 
on top of what is expected during the prior forecast period (12z 
Tue - 12z Wed), local totals within that above corridor will reach 
3-6" over the course of 48 hrs. While this is not a textbook flash 
flood concern, any poor drainage areas and urbanized locales will 
be at the highest risk for flooding during the period. The 
atmospheric river will continue to propagate southward down the 
Pacific coast with a continued threat heading into the D3 period. 
The previous MRGL risk was largely unchanged as the synoptic 
pattern and associated rainfall forecast remains on track. 


Kleebauer
 
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
 

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