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Quantitative Precipitation Forecast (QPF) Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0659Z Jun 04, 2018)
 
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Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Mon Jun 04 2018


Prelim Day 1 QPF Discussion
Valid Jun 04/1200 UTC thru Jun 05/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr



...Northeast...

The elongated, negatively tilted trough nudging into southern
Ontario and the eastern Great Lakes early this morning will become
reinforced by an upper jet streak/additional shortwave energy
entering the trough's base. The result will be a transformation
toward a more positively tilted longwave trough as the low deepens
through the mid-upper levels over southern Ontario-Quebec later
Mon-Mon night. Favorable exit region forcing east of the trough
(upper level divergence and strengthening lower tropospheric s-se
flow and positive moisture/theta-e transport) will favor
additional mod-heavy rainfall along the New England coast, along
the apex of 1.5"+ PWs ahead of the surface occluded front. The
consensus of the 00Z guidance depicted a a decided eastward shift
in the heaviest rainfall during the day 1 period (12Z Mon-12Z
Tue), i.e. mainly offshore Downeast ME while clipping eastern
MA/Cape Cod. While relatively efficient considering the deep
subtropical moisture plume (relatively high wet bulb zero levels
and 500-300 mb layer PW values near 0.25"), the absence of even
elevated instability will be a significant limitation to the short
term rainfall rates with respect to the excessive rainfall/flash
flood threat given the current FFG values.


...Southern Plains...

Southwesterly flow ahead of shortwave trough moving into the Four
Corners region continues to moisten the mid levels across New
Mexico and southern Colorado as southeasterly winds behind a cold
front that has settled southwest into West Texas begin channel low
level moisture into the region.  This will continue to support
developing storms across the mountains before spreading east into
the High Plains this afternoon and evening.  With PW anomalies
increasing to 2-3 standard deviations above normal, there remains
a good model signal for locally heavy accumulations this afternoon
and evening from the southern Colorado and New Mexico ranges
southeastward into the adjacent High Plains of eastern New Mexico
and West Texas.  Forecast confidence diminishes overnight as the
hi-res models show significant spread with respect to how quickly
convection diminishes as it moves further east into central Texas.
 While the NAM CONEST shows widespread moderate to locally heavy
amounts spreading east into central Texas, the HWR-NMMB shows
convection diminishing much sooner with only scattered light
amounts.  WPC QPF reflects a compromise similar to the HREF Mean,
maintaining at least some light to moderate amounts along an axis
of deeper moisture and greater instability across central Texas. 
As the aforementioned shortwave continues to move east, models
continue to differ late in the period with possible convective
redevelopment across central into southeast Texas, with the NAM
CONEST this time being the much drier solution.  With limited
confidence, continued to follow the HREF Mean through the end of
the period.

Hurley