Area Forecast Discussion
Issued by NWS Bismarck, ND

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033
FXUS63 KBIS 301443
AFDBIS

AREA FORECAST DISCUSSION
National Weather Service Bismarck ND
943 AM CDT MON MAY 30 2016

.UPDATE...
Issued at 943 AM CDT Mon May 30 2016

Showers and thunderstorms continue to blossom over western ND this
morning in advance of the shortwave trough seen moving east across
MT on moisture channel (water vapor) imagery. We adjusted PoPs to
reflect ongoing radar trends with this update, and lowered highs
a bit in far western ND where clouds and precipitation will hinder
warming.

The degree of destabilization downstream of the morning convection
is still the main forecast challenge and point of uncertainty with
regard to potential severe weather this afternoon. Modifying the
12 UTC Bismarck sounding for temperatures in the upper 70s F and
dewpoints in the mid 50s F does yield nearly 1500 J/kg of SBCAPE.
Increasing clouds with time and questions about the quality of
moisture return bring uncertainty to the table, so we will launch
a special 18 UTC sounding to try and better gauge destabilization.
That being said, recent HRRR simulations, 00 UTC SPC SSEO output,
and the 09 UTC SREF calibrated severe thunderstorm guidance all
favor south central ND for severe thunderstorms between about 19
and 01 UTC. Note that the 00 UTC SPC SSEO generated a 20 percent
probability of updraft helicity values greater than 100 m2/s2
centered on Sioux and Emmons Counties, which is a statistically
significant probability.

UPDATE Issued at 622 AM CDT Mon May 30 2016

Quick update to blend to observed trends through 11 UTC. Overall,
no change in forecast thinking regarding the severe thunderstorm
and heavy rainfall potential today per the 06-10 UTC high
resolution suites. As highlighted before, how much instability can
build ahead of cloud cover entering western North Dakota will play
a large role in determining the overall severity of the event.

&&

.SHORT TERM...(Today and tonight)
Issued at 405 AM CDT Mon May 30 2016

Severe thunderstorm and heavy rainfall potential today through
this evening highlight the short term forecast.

SPC in their Day 1 Severe Convective Outlook has expanded the
slight risk to include most of southwest and south central North
Dakota. Overall, thunderstorms are expected to enter western North
Dakota late this morning ahead of a surface cold front across
central Montana. This cold front will begin to occlude this
afternoon with a stationary front located across southern Canada
this morning. Thunderstorms will focus across central North Dakota
this afternoon and into the early evening as the cold front
propagates east. Regarding severe potential, the 00 and 06 UTC NAM
solutions have been generally disregarded given low level moisture
fields that are too high resulting in unrealistic CAPE values this
afternoon. The remainder of the 00-08 UTC global and high
resolution suites are plausible. Some uncertainty remains as to
how much surface based instability can build across the southwest
and south central from cloud cover associated with ongoing
convection across Montana. Peak late afternoon ML CAPE values
south central range from 1000-1500 j/Kg on the 07 UTC RAP, to
2000-2500 j/Kg on the 00 UTC GFS, indicative of the uncertainty of
surface heating. Deep layer shear around 35-40 kts is certain
across the guidance sources, supportive of organized convection
especially if the higher bound of instability can be realized.
This is seconded by 2-5 km updraft helicity forecasts from the the
06-08 UTC HRRR and 00 UTC SSE0. Values in excess of 75 m2/s2 have
been depicted by the HRRR, which would support the potential for
supercells. Again, conditional on the higher bounds of instability
being reached, which is uncertain. The main threats with this
event appear to be large hail and damaging winds. However, an
isolated tornado is possible if a discrete supercell structure can
be realized before storms congeal into a line later this
afternoon and evening. WPC does have much of northwest and central
North Dakota in a slight risk for excessive rainfall today and
tonight. Slow storm motions of 10-20 kts are possible today with
PWATs climbing to 1.25 inches. However, the overall threat given
flash flood guidance will likely be confined to urban areas.

.LONG TERM...(Tuesday through Sunday)
Issued at 405 AM CDT Mon May 30 2016

Rain showers Tuesday with a return to dry weather and near normal
temperatures late this week highlight the extended forecast.

The 00 UTC guidance suite is in agreement on an upper level low
across the Northern Plains on Tuesday, supporting the continuation
of widespread rain showers with embedded thunderstorms. Wrap
around moisture on the pivot point of the deformation zone across
northwest and far north central North Dakota may lead to storm
total rainfall amounts Monday through Tuesday approaching two
inches. Thereafter, an intermountain west upper level ridge is
forecast to build into the weekend, marking a return to drier
weather with near normal temperatures.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 943 AM CDT Mon May 30 2016

Widespread thunderstorms will develop in western North Dakota
this morning and spread east through afternoon and evening. Some
storms may be severe with large hail and damaging winds southwest
and south central. Widespread showers with embedded thunderstorms
continue Tuesday with IFR/MVFR ceilings possible.

&&

.BIS Watches/Warnings/Advisories...
NONE.
&&

$$

UPDATE...CJS
SHORT TERM...PJA
LONG TERM...PJA
AVIATION...PJA/CJS



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