Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 190239 CCA
AFDBIS

Area Forecast Discussion...CORRECTED
National Weather Service Bismarck ND
939 PM CDT Tue Jul 18 2017

.UPDATE...
Issued at 939 PM CDT Tue Jul 18 2017

Latest water vapor imagery shows multiple shortwaves across
western Idaho on the nose of a 60kt 500mb jet, continuing to ride
along the northern periphery of a broad upper level ridge. These
shortwaves and jet will reach western ND late tonight/early
Wednesday morning, followed by a more distinct 700mb-500mb
shortwave Wednesday afternoon moving across southern ND.

Soundings and latest CAM`s indicate increasing coverage of
elevated thunderstorms late tonight/early Wednesday morning as a
low level jet increases across western ND. This is then expected
to morph quickly into a large area of showers and thunderstorms
Wednesday morning, pushing quickly across central ND. Some severe
weather is possible. Another round of possible severe weather
would come in the afternoon with the aforementioned midlevel
shortwave, mainly affecting locales along and south of Interstate
94. Convection will be rather messy in the morning, and that will
play a role in how things evolve/destabilize in the afternoon,
especially if cloud cover holds in. The latest 21z SREF calibrated
severe thunderstorm has taken a noticeable uptick in the
probability of severe thunderstorms in southern ND Wednesday.
After collaborating with SPC, we will be mentioning some severe
thunderstorm wording in the gridded data and text products.

UPDATE Issued at 537 PM CDT Tue Jul 18 2017

Local/Regional radars indicative of a few supercells in southeast
Montana at this time. The experimental HRRR seems to have some
signal on what is occurring, with a couple splitting storms taking
shape as they edge closer to our southwest border. Thus far, dime
size hail being reported in southeast MT, along with gusty winds
(sub severe at this time). Mixed layer cape sufficient between
1000 and 1500 J/Kg, with strong deep layer shear between 30kt and
50kt. DCAPE/Downdraft Cape on the order of 1200 J/Kg, so isolated
damaging winds possible and will continue to monitor very closely.
Adjusted pops based on current radar, movement, and forecast into
southwest ND through 03z. Rest of forecast elements looked good.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 401 PM CDT Tue Jul 18 2017

Late this afternoon and this evening an isolated thunderstorm or
two is possible in the southwest. The SPC day 1 convective outlook
has the far southwest corner in a marginal risk for a severe
storm. The current ECMWF/GFS/RAP are indicating ample 0-6 km bulk
shear with values around 60 kts but the low/mid level lapse rates
and CAPE values are not impressive. Any chance for severe
thunderstorms in the southwest appear to be slight. The CAMS are
scattered with only the HRRR hinting at something in the southwest
around 22Z.

As we get into Wednesday, an embedded pulse in the zonal flow aloft
will result in chances for another round of showers and
thunderstorms. SPC has most of the south in a marginal risk for
severe storms. Severe weather ingredients look more promising for
storms becoming strong to severe. Additionally, the current suite
of ensemble and deterministic models are in good agreement on an
area of QPF moving from the west to southeast through the day. The
WPC day 2 QPF valid for Wednesday has between 0.10 and 0.25
inches of rain for much of western and central ND. West central
and south central areas are painted with values between 0.25 and
0.75 inches of rain. Locally higher amounts are possible with
thunderstorms.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 401 PM CDT Tue Jul 18 2017

Most of the action for the extended will come Thursday evening
through Friday, as a weak wave aloft will bring chances for showers
and thunderstorms. The SPC day 3 convective outlook has most of
western and central ND highlighted in a marginal risk for severe
thunderstorms. The 12Z ECMWF/GFS convective parameters for Thursday
are sufficient for the development of strong to severe storms.

The outlook for the rest of the long term, a chance or two for a
thunderstorm and near seasonal temperatures.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 537 PM CDT Tue Jul 18 2017

This Taf period, will be monitoring for a potential round of
showers and thunderstorms, possibly heavy and/or severe, during
the daylight hours Wednesday. Indications are that an area of
thunderstorms couple develop over eastern Montana 09z-12z
Wednesday, then quickly shift across western and central ND 12z-
21z Wednesday. Low confidence on timing and complete evolution of
thunderstorms for any one terminal. Thus for now, have not carried
any predominate mention of thunderstorms and/or intensity, but
have mentioned a vcts during the expected timeframe. Will await
the model guidance later this evening for better continuity and
confidence.


&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...KS/AE
SHORT TERM...AC
LONG TERM...AC
AVIATION...KS



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