Flash Flood Watch 4, NWS Goodland, KS

Area Forecast Discussion
National Weather Service Goodland KS
542 PM MDT Sun Aug 6 2017

.SHORT TERM...(This afternoon through Monday)
Issued at 205 PM MDT Sun Aug 6 2017

NW flow aloft transitions to more of a west-southwest flow, with a
coupled upper level jet structure forecast to build over the Central
High Plains late tonight through Monday. Moist southeast flow will
continue to feed into the region, and as upper level forcing
increases widespread showers and thunderstorms should develop from
the west to the east overnight tonight. I can't rule out an isolated
thunderstorm this afternoon, but with subsidence in place at this
time and main forcing still well west before 00Z it's hard to say
where this would be favored. There might be a brief period of
subsidence in the afternoon Monday between mid level vort maxes that
could create a lull for parts of our CWA, but we may still have
lingering showers across our west and only a decrease in intensity.

Regarding severe threat: SPC Mesoanalysis already shows 1500 J/KG ML
CAPE along CO/KS border, match trends from earlier RAP and through
the early evening moderate instabilty may be in place. Bulk
Effective shear is forecast to be in the 30-45kt range, so there
could be a window for a few organized severe cells before
instability drops off before 03Z. Favored locations are going to be
west based on expected thunderstorm timing/favored location during
this limited window.

Regarding heavy rain threat: PWATs 1-1.5" will combine with
favorable thermal and "skinny" CAPE profiles to support very
efficient rain processes. Models are showing strong overlap with
high QPF across our west for the 36hr period. Considering the
potential for slow thunderstorm motion or backbuilding we could have
localized flash flood threats. The question will be how widespread
and where if there is a heavy rain threat, with instability  limited
at times across our CWA. Ultimately this may end up being a
prolonged moderate rain event where the totals are spread out, and
instantaneous rates remain less than flash flood guidance. I leaned
against a flash flood watch during this update, but I did play up
wording in both forecast and HWO.

.LONG TERM...(Monday night through Sunday)
Issued at 205 PM MDT Sun Aug 6 2017

Shower and thunderstorm chances persist throughout the long term
period as weak shortwaves move through the west to northwest flow
aloft.

A stronger disturbance continues across the High Plains from the
Rockies Monday night through Tuesday night, generating showers and
thunderstorms. With abundant moisture filtering into the region and
PWATS in the 1 to 1.5 inch range, locally heavy rainfall will be a
concern during this timeframe and flash flooding will need to
monitored.

Conditions dry out midweek behind the passing disturbance, but with
persistent northwest flow, patchy precipitation chances are strewn
throughout the forecast area. Predictability of locations and timing
are made difficult by the variability of this weather pattern. It is
even tougher to have confidence in periods further out. That being
said, guidance suggests that a shortwave will travel through the
Plains at the end of the work week as a cold front approaches from
the north, crossing the area by Sunday. Cannot rule out
precipitation through the weekend.

Temperatures gradually warm during the long term period, but remain
below normal. Highs start in the low/mid 70s on Tuesday and climb
into the low/mid 80s by Friday. Lows remain in the mid 50s to low
60s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 533 PM MDT Sun Aug 6 2017

VFR to IFR conditions forecast for the TAFs. Primary focus is the
timing of rainfall and associated lower ceiling. Have more
confidence of when the rainfall/low ceiling will begin and duration
for KGLD than KMCK. May end up needing to place rainfall in a
prevailing group for KMCK, but do not have high enough confidence
for this TAF. Moderate to heavy rainfall is likely to occur at
KGLD during the overnight, just not enough confidence of when an
how long it will last to mention in this TAF. For both sites the
ceiling may be IFR longer into the morning than currently
forecast, but have ceiling improving based on trends this morning
and what is typical for both sites.

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

SHORT TERM...DR
LONG TERM...JBH
AVIATION...JTL

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