Graphic for MPD #0012

Mesoscale Precipitation Discussion 0012
NWS Weather Prediction Center College Park MD
506 PM EST Fri Jan 12 2024

Areas affected...northern Mid-Atlantic region

Concerning...Heavy rainfall...Flash flooding possible

Valid 122200Z - 130400Z

SUMMARY...Areas of moderate to heavy rain are expected to
translate northward through the Mid-Atlantic region late this
evening and early tonight. Occasional hourly totals over 0.5
inches will be possible and 1 to 1.5 inches in 3 hours where
training occurs. Given wet antecedent conditions due to recent
above average rainfall, localized excess runoff/flooding will be
possible.

DISCUSSION...2130Z radar imagery showed pockets of moderate to
heavy rainfall occurring from the western Carolinas into portions
of southern VA near the Blue Ridge Mountains. CIRA LPW imagery
showed strong low to mid-level moisture transport was occurring
from the south ahead of an occluded cyclone analyzed over the TN
Valley and Southeast at 21Z, with 925-850 mb mean layer winds
ranging from 40-60 kt across the Mid-Atlantic states, supporting a
rapid increase in total precipitable water. As an example, the
PWAT value at Columbia, SC increased from 0.3 to 1.0 inches over
the past 6 hours according to GPS data.

The RAP has been consistent with the axis of strong moisture
transport along the East Coast late this evening, supported by
strengthening 925-850 mb winds peaking in the 70-80 kt range from
eastern VA into the Delmarva Peninsula by 05Z, increasing PWAT
values to near 1 inch along the I-81 corridor and up to 1.3 inches
along the I-95 corridor from RMN to PHL. An SW to NE axis of low
level convergence is likely to set up along the leading edge of
the stronger low level winds, near or just west of the I-50
corridor from DCA to PHL, which will be parallel to deeper layer
steering flow. Additional forcing due to upslope flow into the
Blue Ridge and central Appalachians is expected to support locally
higher rainfall rates as well. MUCAPE will increase up to a couple
hundred J/kg according to the past few cycles of the RAP in the
vicinity of the I-95 corridor, which while weak, may still support
some hourly rainfall totals over 0.5 inches and 3 hour totals of 1
to 1.5 inches due to training/repeating areas of heavy rain. Given
very wet antecedent conditions due to recent heavy rainfall and
many areas streams/rivers running above normal, excess runoff from
heavy rain may lead to a few areas of isolated flooding, perhaps
focused best across low lying and urban locations that experience
poor drainage.

Otto

ATTN...WFO...AKQ...BGM...CTP...LWX...PBZ...PHI...RLX...RNK...

ATTN...RFC...MARFC...OHRFC...SERFC...NWC...

LAT...LON   41287682 40837574 40037521 39347605 38777680
            37627810 37317921 37318007 37958053 39367964
            40487878 41187805
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Last Updated: 506 PM EST Fri Jan 12 2024