The Weather Prediction Center
College Park, MD
Quantitative Precipitation Forecast
Discussion
[Abbreviations and acronyms
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Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
532 AM EDT Tue Jun 05 2018
Final Day 1, Day 2 and Day 3 QPF Discussion
Valid Jun 05/1200 UTC thru Jun 08/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr
Day 1
...Northern Plains - Upper Mississippi Valley...
Upper ridge axis pushes east of the northern Plains and Upper MS
Valley region Tue night. In its wake, an uptick in broad scale
upper forcing (divergence aloft) will ensue, and get a
considerable boost within the right entrance region of an upper
level jet streak traversing southern Ontario. Meanwhile, the
increasing (and veering) nocturnal LLJ will lead to rapid
low-level moisture/theta e transport ahead of a sharpening frontal
zone. Both synoptic and thermodynamic indicators give credence to
the the multi-model signal of a developing MCS overnight along the
"ring of fire", though as is typical, the model solutions are not
well clustered with respect to the details in terms of MCS track
and thus axis of heaviest rainfall. WPC did nudge the QPF axis a
little father south from the previous forecast -- essentially in
line with the blend of the WRF-ARW, ARW2, and NSSL-WRF (all of
which aligned reasonably well, while the NAM CONUS Nest, WRF-NMMB,
NBM, and global guidance were farther north. Despite the fairly
vigorous mid-level cap, based on climo like the aforementioned
high-res depiction of the heavy rainfall footprint farther south,
along and north of the surface boundary where the coupling of
robust deep-layer elevated instability and moisture transport will
be maximized north-northeast of the 700 mb +12C isotherm. Also
supporting a more southern solution of the MCS track/heaviest QPF
would be the degree of southward propagation overnight, as the
s=sw LLJ begins to exceed the speed of the mean 850-300 mb flow.
At this point, the progged shear profiles would support a
progressive MCS; however, multiple rounds of convection as noted
from the ARW/ARW2 (first one along the initial wnw-ese warm
frontal boundary) could pose a more enhanced flash flood risk
across far northeast SD and southeast ND.
...Central Gulf Coast Region...
Mid-upper shortwave trough -- bolstered early in the period the
MCV over the ARKLATEX -- will be the catalyst for additional
diurnally-enhanced convection along the surface stationary front
south toward the Gulf coast. 0-6km bulk shear values aoa 25 kts
along with robust deep-layer instability (mucapes at 2000-3000+
j/kg) will support more organized, widespread coverage during the
afternoon through mid evening ahead of the upper trough, with the
surface moisture convergence getting an added boost from the
developing Gulf breezes. Despite the relatively high 1-3 hourly
FFG (generally 2.5-3.0" in 1 hour and 3-4" in 3 hours), localized
totals of 3-5" within a few hours per the high-res CAMs would
support a marginal risk of excessive rainfall, particularly over
portions of se LA given the relatively wetter antecedent soils
(lower FFG values).
Hurley
Day 2
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER THE CENTRAL
PLAINS...
...Northern Rockies to Central Plains...
Weak shortwave energy rounding a broad mid-upper level ridge axis
extending up the high plains will cross the north-central Great
Plains Wednesday. A low level jet under the ridge will bring Gulf
moisture north with 1.5 inch PW over NE/IA which is two standard
deviations above normal. The combination of high moisture,
instability, and mid level forcing should be enough to break the
cap and trigger scattered heavy thunderstorms that will shift
southeast in the anticyclonic flow. MCS development is likely
given the strong instability and expected forward propagation.
QPF was based on a blend of the 00Z GFS/NAM/ECMWF and in-house
bias-corrected blend. The marginal risk is for the main convective
storm breeding ground east of the Sand Hills where 6-hr FFG is
generally 2 to 2.5 inches. Progression of organized/MCS activity
may need to be accounted for in subsequent QPF and ERO.
...Florida...
A swath of 1.75 inch PW along a stalled front will allow heavy
rain across central FL. Light easterly mean flow could allow
repeating cells off the Gulf. FFG is quite high in central FL, so
flash flooding is likely limited locally.
Day 3
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER THE CENTRAL
PLAINS AND NORTHERN HIGH PLAINS...
...Northern Rockies to Central Plains...
Weak shortwave energy rounding a broad mid-upper level ridge axis
extending up the high plains will cross the northern Great Plains
Thursday. A wake from Wednesday activity should exist over the
north-central plains Thursday with development likely initiation
along remnant boundaries. 1.25 to 1.5 inch PW is 1.5 to 2 standard
deviations above normal. Instability is progged to be stronger
over the Central Plains then MT which may allow for greater MCS
development. More details on mesoscale processes on subsequent
forecasts.
QPF was based on a blend of the 00Z GFS/NAM/ECMWF and in-house
bias-corrected blend. The marginal risks over MT and NE/KS/IA is
based on 00Z consensus for the low position along with more
sensitive FFG.
Hurley/Jackson
Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml
Last Updated: 532 AM EDT TUE JUN 05
2018