Scientific Forecaster Discussion

Return to Local Conditions & Forecast
Area forecast discussion 
National Weather Service Bismarck ND
1230 PM CDT Friday Apr 18 2014

Update...
issued at 1230 PM CDT Friday Apr 18 2014

Only updated the hourly sensible weather grids based on current
obs/trends. The current Wind Advisory headline looks to be in good
shape. The freshened up products have been sent.

Update issued at 1000 am CDT Friday Apr 18 2014

Winds are beginning to pick up over portions of central and
eastern North Dakota this morning. The current Wind Advisory
headline looks good so will not adjust for this update.

Otherwise...only changed precipitation wording from uncertainty to
coverage for this afternoon. No other adjustment were required.
The updated gridded and text products have been sent.

Update issued at 627 am CDT Friday Apr 18 2014

Forecast is on track and only change was to match forecast
elements to latest observation. Radar showing some weak returns across
Montana...while surface observation show southeast winds strengthening
across most of County Warning Area.

&&

Short term...(today and tonight)

Issued at 402 am CDT Friday Apr 18 2014

Forecast highlights in the short term period will be strong winds
developing this morning and afternoon...chances for rain now
through tonight...and the possibility of a thunderstorm far
southwest/far south central later today into this evening. Models
in fair agreement and based the short term period on a blend.

Currently...upper level ridge axis over the High Plains moving
eastward as a potent shortwave trough over the Pacific northwest
propagates inland. Lee side cyclogenesis underway across Alberta
southward across Montana in response. Broken-overcast clouds continue to
stream across the local area ahead of the ridge. Increasing
thermal upglide east of the developing surface low resulting in radar
returns across the region. Ceilings generally 8k feet above ground level and up so
doubt much is reaching the ground. The exception is the northwest
corner of the state where ceilings have dropped to 4k feet above ground level with kisn
reporting light rain periodically this am. This is also where the
strongest thermal lift is at and moisture advection.

For precipitation over the next 24 hours or so...will generally
see chances increasing across western North Dakota today spreading
east across the remainder of the forecast area this evening as the
upper level trough/middle level low moves east across northern
Montana and the surface low and its associated frontal boundaries move
east across the Dakotas. Strong warm air advection this afternoon/evening across
western and central South Dakota will nose into my South Dakota
border counties generating late afternoon/evening destabilization.
4km WRF indicates a weak convective complex developing over far
southeastern Montana and advancing east-northeast for several
hours. Thus added thunderstorms to the forecast 22z-06z late this
afternoon and evening far southwest and far south central.
Precipitation will end after midnight as forcing associated with
the upper level wave and surface low move more into far eastern ND and
Minnesota. Expect quantitative precipitation forecast to remain at or below a quarter of an inch
with the heavier precipitation remaining off to our north closer
to the middle level low.

Southeast winds already on the increase right now as the pressure
gradient continues to tighten east of the deepening surface low. A
rather impressive pressure gradient will materialize for
today...generating sustained southeast winds around 30 miles per hour and
gusts to 40 miles per hour across my central and east. Thus have hoisted a
Wind Advisory from this morning through the afternoon (through middle
evening across the James River valley) where winds are expected to
be strongest. There may be a period where strong winds will occur
across the southwest this morning/early afternoon. Will monitor.

Long term...(saturday through thursday)
issued at 402 am CDT Friday Apr 18 2014

Period begins with progressive pattern and quasi zonal
flow across northern Continental U.S. With strong short wave skirting just
along international border...supporting surface low and associated
precipitation departing to east of County Warning Area. Another shortwave follows similar
path...but best precipitation chances remain north of the border Sunday
into Monday. However...NAM/ECMWF show weak instability with cold
front crossing the area during the afternoon. Therefore have
included some low probability of precipitation and slight chance of thunder across mainly
central and northwest areas Sunday afternoon. This shortwave then
digs across Great Lakes region while ridge builds across western
Continental U.S. By Monday. This more amplified pattern continues with long
wave trough moving into the west on Tuesday. At this point model
differences begin to increase with progression of upper low to
approximately Montana by 00z Thursday...where 00z GFS cuts off low while
00z European model (ecmwf) and GFS ensembles are in better agreement with an open
trough. Regardless of these differences...overall pattern supports
higher probability of precipitation beginning Tuesday night. Some question about extent of
instability with GFS/European model (ecmwf) showing very weak instability nudging
into ND Wednesday. Given model differences and run/run
changes...tapered down on thunder chances but did not remove
entirely.

&&

Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1230 PM CDT Friday Apr 18 2014

VFR conditions will prevail over western and central North Dakota
through the taf period. Windy conditions will also continue
through early evening...with gusts up to 40 knots possible. Light
showers and tempo MVFR conditions could impact kisn-kmot later
this afternoon and evening. However...brief rain shower activity
is expected. Brief scattered showers will also be possible over
the I-94 terminal aerodromes this afternoon and evening. This
activity will taper off from west to east after midnight tonight.

&&

Bis watches/warnings/advisories...
Wind Advisory until 7 PM CDT this evening for ndz003>005-011>013-
021-022-035.

Wind Advisory until 10 PM CDT this evening for ndz023-025-036-
037-047-048-050-051.

&&

$$

Update...tm
short term...New Hampshire
long term...jns
aviation...tm