Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Bismarck ND
950 PM CDT Sat Aug 30 2014
issued at 950 PM CDT Sat Aug 30 2014
The severe threat has moved east along with the surface boundary.
As a result...removed Billings...slope...and Bowman counties from
the Severe Thunderstorm Watch. A cluster of thunderstorms capable
of producing winds around 40 miles per hour are slowly moving east across
Hettinger and Adams counties south of Dickinson. The severe threat
remains for the counties still in the watch...although it is
diminishing with the loss of daytime heating. The updated products
have been sent.
Update issued at 758 PM CDT Sat Aug 30 2014
Updated all products to add Severe Thunderstorm Watch 478 to the
southwestern zones. The watch is in effect until 2 am CDT / 1 am
MDT Sunday. The main threats will be damaging winds and large
hail. The updated products have been sent.
Update issued at 632 PM CDT Sat Aug 30 2014
Based on the latest radar observation/trends and hi-res model
output...slowed the eastward progression of convection currently
over western North Dakota by a few hours.
The latest laps analysis indicates surface-based cape values
between 1000-1500 j/kg currently nosing into southwestern North
Dakota. Furthermore...Storm Prediction Center mesoanalysis indicates 0-6 km shear
around 40 knots. The environment is becoming more favorable for
severe weather this evening. However...the increasing high clouds
is likely The Fly in the ointment keeping convective initiation to
a minimum as of the time of this writing. Will continue to monitor
convective trends and adjust the forecast as needed. For now will
keep severe mention in the southwestern zones for this update. The
other forecast elements are in good shape.
Short term...(this evening through sunday)
Issued at 317 PM CDT Sat Aug 30 2014
Current surface analysis places low over north central Wyoming
while frontal boundary drops through central Montana. Upper level
analysis places broad trough over the western Continental U.S....with initial
short wave lifting through northeast Montana into northwest North
Dakota. Secondary wave now pushing through central Montana/eastern
For the rest of this afternoon into this evening...initial short
wave will continue to slowly lift towards the northeast bringing
showers and possibly a few claps of thunder to northwestern North
Dakota. Main concerns come later on as aforementioned secondary
wave makes its approach...pushing into the western part of
the state towards late afternoon/early evening before moving
through the area. The timing of this wave will coincide with the
strongest instability developing over southwestern North Dakota
(1-1.5 kj/kg cape values) combined with adequate deep layer shear
to support rotating updrafts. Therefore...the possibility of
severe weather remains over this area. Wave will continue its
eastward progression through the state overnight with models in
good agreement showing widespread rainfall through the area. Expect
some storms may have locally heavy rainfall but with storms
expected to be moving at a good clip do not have widespread
flooding concerns at this time.
On Sunday...any linger precipitation should be coming to an end around
sunrise. Next wave moving through cyclonic flow approaches the area
towards middle-day bringing the next chances for precipitation...though
coverage should only be isolated to scattered.
Long term...(sunday night through saturday)
Issued at 317 PM CDT Sat Aug 30 2014
Broad middle level trough will result in a cool cyclonic flow aloft
through Monday night producing scattered showers and thunderstorms
and below average temperatures...with highs for Labor Day in the
upper 60s to middle 70s. Flow transitions momentarily to zonal and
should result in a dry period later Monday night through Wednesday
afternoon. By mid-week...flow becomes more southwesterly when
another middle level shortwave moves east across the northern plains and
south central Canada. Medium range models then keep the upper jet
stream over the region through the remainder of the work week. Saw
no reason to deviate from CR allblend probability of precipitation with the jet stream
aloft and the possibility of embedded energy in the west-
southwesterly middle level flow depicted through the extended.
We still do not see any big weather problems with this flow other
than scattered thunderstorms early in the week and towards the
second half of the week.
Getting that time of year when frost becomes more of an issue. At
this time nighttime dewpoint temperatures are forecast to remain
in the 40s through the first week of September so morning lows
should remain well above those values where frost would develop.
Latest 12z European model (ecmwf) does indicate a rather strong cold for next
Saturday with the 850mb 0c degree isotherm near the Canadian
border...but is an outlier compared to previous runs and other
models. Will of course monitor to see if this particular run
gains support from other guidance next day or so.
Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 632 PM CDT Sat Aug 30 2014
Scattered to numerous showers and thunderstorms will develop from
west to east tonight. Visibility restrictions are expected in heavier
precipitation. Some severe storms will be possible mainly over
southwest ND this evening. Behind the precipitation...widespread
MVFR/IFR ceilings are expected mainly over southern and central ND.
Conditions will improve to VFR later Sunday morning.
long term...New Hampshire