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787
FXUS63 KBIS 201118
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
618 AM CDT Sun May 20 2018

.UPDATE...
Issued at 514 AM CDT Sun May 20 2018

No notable changes made with this forecast update. Blended in the
current observations.

&&

.SHORT TERM...(Today and tonight)
Issued at 215 AM CDT Sun May 20 2018

Clear skies and dry weather highlight the short term forecast,
with widespread early morning frost.

The latest observed surface weather map over western and central
North Dakota shows a 1024 mb high pressure system centered over
the area. This will lead to the continuation of clear skies and
calm weather today and tonight. Given the clear skies and light
winds, expect widespread morning frost across most of western and
central North Dakota through 8 AM CDT as temperatures drop down
into the 30s near sunrise.

Although minimum afternoon relative humidity values will be quite
low across northern North Dakota today, southerly winds do not
look strong enough for any fire weather concerns.

.LONG TERM...(Monday through Saturday)
Issued at 215 AM CDT Sun May 20 2018

A warming trend with the return of showers and thunderstorms
highlight the long term forecast.

A split-flow synoptic pattern will dominate on Monday, with a
large upper-level low over southern California and near zonal flow
across North Dakota. Forecast NAM/GFS BUFR soundings show plenty
of dry air throughout the troposphere across western and central
North Dakota on Monday, leading to mostly clear skies and calm
weather. High temperatures on Monday were manually increased
by a few degrees into the mid to upper 70s across all of western
and central North Dakota, as the latest blend of model guidance
suggested temperatures a bit too low considering the ECMWF MOS
guidance and a well-mixed boundary layer with plenty of sunshine.

The 00z iterations of both the GFS and the ECMWF show a shortwave
moving through western North Dakota Tuesday afternoon, bringing
with it a chance for thunderstorms. Widespread severe weather is
not expected on Tuesday at this time, however some uncertainty
remains. The GFS suggests 0 to 6 km bulk shear values between 30
and 40 kts across western North Dakota, with CAPE near 500 J/kg
across the northwest and near 2000 J/kg across the southwest. The
ECMWF paints a less concerning picture, with only 20 to 25 kts of
shear and CAPE between 500 and 800 J/kg. Forecast BUFR NAM
soundings show higher CAPE values comparable to the GFS, however
the shear is very similar to the ECMWF at only 20 to 30 kts. With
a surface frontal boundary located over eastern Montana Tuesday
afternoon, the biggest severe threat looks to be outside of
western and central North Dakota at this time.

Chances for showers and thunderstorms will continue on Wednesday
through Friday as multiple waves move through western and central
North Dakota. Both the GFS and the ECMWF suggest shear that is
generally too weak for widespread severe weather on Wednesday
through Friday, however a few stronger storms cannot be ruled out
given modest to high instability. The timing of frontal boundaries
moving through the area will need to be monitored, as this could
increase or decrease the threat of severe weather.

Saturday and Sunday look to be dry with slightly above average
temperatures as an upper-level ridge builds in from the west.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 617 AM CDT Sun May 20 2018

Clear skies and calm weather across North Dakota will lead to VFR
cigs and visibilities through the end of the forecast period for
all terminals.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 9 AM CDT /8 AM MDT/ this morning for
NDZ002>005-010>013-018>023-031>036-040>047-050-051.

&&

$$

UPDATE...TK
SHORT TERM...TK
LONG TERM...TK
AVIATION...TK