FOUS30 KWBC 151906
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
306 PM EDT Sun Mar 15 2026
Day 1
Valid 16Z Sun Mar 15 2026 - 12Z Mon Mar 16 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST PENINSULAR FLORIDA...
16Z Update...
The previous forecast remains largely on track based on the latest
12Z HREF/06Z REFS guidance and recent HRRR solutions which
continue to depict small-scale clusters of locally heavy showers
and thunderstorms across the central and southern portions of the
FL Peninsula. The Marginal Risk for the more sensitive southeast FL
urban corridor will be maintained.
Satellite and radar imagery shows convection rapidly developing and
expanding across portions of the Midwest ahead of the deepening low
center transiting the region. Very progressive cell-motions are
still expected to generally keep rainfall totals to a modest level
at least through this afternoon. There may be some potential for
some localized cell-training with convection associated with the
low track this evening across areas of northern IL, northwest IN
and into southwest Lower MI, but the latest guidance generally
indicates rainfall amounts through this evening peaking in the 1 to
2 inch range. The latest FFG exceedance probabilities here are
very low, and therefore we will continue to hold off on any upgrade
to a Marginal Risk. However, conditions will be closely monitored
with today's expected organized convective outbreak. If guidance or satellite/radar trends support heavier short-term QPF, an upgrade
later today or early this evening could still be necessitated.
Orrison
Previous discussion...
A very strong dynamic cyclone will be in full force across the
Upper Midwest and Upper Great Lakes with a strong attendant cold
front crossing out of the Plains through the Lower Ohio and
Mississippi Valley. The strength of the low level flow prior to the
cold front will draw modest moisture through the Valleys to provide
1-1.25" Total PWat values. The focus will be on severe aspects of
the convective line and there will be some stronger updrafts and
solid moisture flux convergence associated with these convective
cores capable of sub-hourly to hourly rates/totals in the vicinity
of 1-1.5"; the duration will be brief to limit overall totals to
less than 2" overall. This could result in random, widely spaced
incident or two of flash flooding, but limited to urban and
traditionally flood prone locations. So while there is a non-zero
risk of excessive rainfall, it remains below the 5% coverage for a
Marginal Risk to be delineated at this time but will continue to
monitor trends for subsequent updates.
Further southeast, the draw of moisture out of the Caribbean
through the Strait of Yucatan will draw higher moisture though the
eastern Gulf. Combined with return easterly flow north of the
Greater Antilles into the Bahamas; there is an increase in
moisture confluence (total PWats to 1.75") through Peninsular
Florida. Onshore flow from the southeast and clearing skies will
allow for some increased instability (1250-1500 J/kg) to build for
thunderstorm activity across the southern Peninsula before evening.
Rates in excess of 2"/hr may result in highly localized spots of
2-5" that may result in localized rapid inundation flooding if over
the southern I-95 urban corridor. Converging sea-breezes may also
result in mergers across the central Peninsula from north to south,
but are likely to be more intense initially but also much more
brief relative to those closer to coastal convergence zones that
may allow for longer duration. HREF probabilities of 3-5"/24hrs are
sufficient to highlight a small Marginal Risk of Excessive
Rainfall.
Gallina
Day 2
Valid 12Z Mon Mar 16 2026 - 12Z Tue Mar 17 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC AND NORTHEASTERN U.S & EXTREME NORTHWEST
WASHINGTON...
19z Update: Forecast looks on track. Nothing in the 12z high res=20
guidance supports any changes to the inherited Marginal risk=20
areas.
Chenard
...Mid-Atlantic into Northeast...
Highly meridional moisture surge will be already ongoing at the
start of the forecast period (16.12z) as the leading edge of the
Atlantic warm front should be lifting through southern New England
and Gulf of Maine. Upstream the highly dynamic cyclone will be well
occluded through depth across the north-central Great Lakes with a
powerful near 980mb surface low and attendant sharp cold front
extending due south across the Mid-Ohio Valley, Cumberland Plateau
into the central Deep South. The based of the large scale trough
will be lifting northeastward providing solid dPVA to support
strengthening deep layer southerly flow further compounding on the
initial warm advective surge through out of the Southeast through
the Mid-Atlantic. Integrated Vapor Transport (IVT) values will
increase from upper hundreds of kg/m/s toward 1250 kg/m/s across
the Coastal Plain into southern New England eventually reaching
values over 1400 kg/m/s after 00z through S ME due to the combining
strength of the LLJ and confluent moisture streams off the Eastern
Gulf and Western Atlantic. This brings moisture flux well above
97-99th+ percentiles of moisture flux. Instability will be a
limiting factor for vertical development along/ahead of the cold
front but some 250-750 J/kg will be available through the central
Mid- Atlantic with some localized convergence for scattered showers
and thunderstorms prior to the main cold front/squall line to
emerge out of the Appalachian terrain by mid-day. These initial
cells should be quick moving and limited in total, but any that
broaden into stronger isolated super-cells may have capability for
locally intense rates prior to the main line. Still, the main focus
will be the hourly to sub- hourly 1-1.5+" totals with the main
convective line that will have greatest potential for localized,
mainly minor flash flooding impacts.
Hydrologically, the Northeast remains highly saturated and cold
through depth with modest SWE in some remaining snow pack. So,
while the rain rates will likely be much lower due to lack of deep unstable/vertical shower activity; the orographic ascent and should
remain concerning that any rain on snow will further compound the
ongoing hydrologic/stream rises (please refer to National Water
Center FHO and Local River Forecast Center forecasts for further
river concerns across this region).
As such a broad Marginal Risk will remain in place for nearly all
of the Northeast (minus areas in south to south-southwest rain
shadow areas of far N VT), with an extension of the Marginal into
the Potomac River Valley and southern extents of the Megalopolis
where those higher rates/short-burst totals may result with
localized exceedance of lower hourly FFG values.
...Pacific Northwest...
Prolonged warm advection of a moderate positively anomalous
moisture stream will be continuing across the extreme northwestern
portion of the Olympic Peninsula with a very weak continuation to
the northern Washington Cascades. Rates will remain fairly
consistent between .25"-.33"/hr allowing for totals to near 3-5"
toward the the end of the forecast period with 00z HREF probability
of 5" nearing 30%; though 5"/24hr just across the Sound will be
near 60%. By late evening/early overnight period, the cold front
will be starting to surge southeastward and further direct enhanced
moisture flux toward the Olympic Peninsula after 06z, with 1-1.25"
Total PWats fluxed on 40-45kts of flow generally resulting in about
750 kg/m/s IVT values, bringing rates locally up to .5" for the
best orographic ascent regions. As such, a very small Marginal Risk
was included for this AR surge into an area already at above
average soil saturation due to recent AR plumes in the last few
days/week(s).
Gallina
Day 3
Valid 12Z Tue Mar 17 2026 - 12Z Wed Mar 18 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHWEST WASHINGTON...
19z Update: Marginal risk looks on track, thus no changes needed.
Chenard
At the start of the day 3 forecast period, 18.12z, the strong,
prolonged Atmospheric River had recently shifted slightly eastward
directing the core of the AR plume centered across Northwest
Washington into the northern Cascades, oriented from SW to NE. Deep
layer moisture remained well above normal with total PWat values
remaining well above 1" with 1.25" reaching the southwest flanks of
the Olympic Range. Winds had calmed a tad but remain around or
above 40kts through the 850-700mb range favorably orthogonal to the
Olympic Range. Freezing levels are well above even the highest
peaks, exposing some Snow Water Equivalent (SWE) to the higher WAA southwesterly flow adding to the .25"-.33"/hr rain rates though
will be higher earlier in the period as winds slack ever so subtly
between shortwave features. Overall IVT values will remain above
500 kg/m/s with peak values over 750 that extend into the northern
Cascades as well. As such, 24hr totals will once again be over 3-4"
and combined with the snow melt, could further increase stream
flows. With lower rates, a Marginal Risk of Excessive Rainfall will
remain in place; however, please refer the National Water Center
and NWRFC forecasts for stream/river flow/rise information with
respect to increasing flooding potential.
Gallina
Day 1 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!91M5cz7d7XyX5j7s0jTmOCPXKmQDcCCVxTJFAlC7pVfp= Eqtw3MYO3vgft-3Yv2QFkr7gjzLYru-q9-GlwGsbRQcBWMc$=20
Day 2 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!91M5cz7d7XyX5j7s0jTmOCPXKmQDcCCVxTJFAlC7pVfp= Eqtw3MYO3vgft-3Yv2QFkr7gjzLYru-q9-GlwGsb4JHlIUQ$=20
Day 3 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!91M5cz7d7XyX5j7s0jTmOCPXKmQDcCCVxTJFAlC7pVfp= Eqtw3MYO3vgft-3Yv2QFkr7gjzLYru-q9-GlwGsbwXaLSS0$=20
=3D =3D =3D
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