Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Forks ND
945 PM CDT Thursday Jul 24 2014
issued at 944 PM CDT Thursday Jul 24 2014
Water vapor loop indicated upper level low pressure system was over
southern Alberta. Upper level system will drive a cold front across the
western Dakotas late tonight and into the forecast area Friday.
Precipitable water rises to around an inch and a half by morning.
Good surface mixing ratios precede frontal system in the west.
However not much of a low level jet forecast precedes front for
tonight. However stronger jet is out of the northwest and is Post
Models indicate two 700 Theta-E ridges over the forecast area and
the other in western ND/eastern Montana. Model soundings indicate 850 hpa
dewpoints increase overnight in southeast zones. Radar indicating
precipitation trying to develop over southeast zones. Both GFS and European model (ecmwf)
develop precipitation over southeast zones. Will increase probability of precipitation in southeast
Update issued at 700 PM CDT Thursday Jul 24 2014
Radars indicated band of precipitation moving into Barnes, Griggs, and
Nelson counties. Precipitation was moving east about 50 knots. Lightning
network indicated activity has decreased to no recent lightning
strikes. Expect precipitation to continue moving east and dissipating. No
changes made to current forecast.
Short term...(this evening through Friday night)
issued at 315 PM CDT Thursday Jul 24 2014
Forecast challenge concerns T chances and temperatures. Models in
fair agreement however showing differences in precipitation coverage
location with next short wave. At this point European model (ecmwf) having best
handle on current rain location so will follow in the near term.
Shortwave to rotate around upper low tonight which will reach
western Canadian prairie provinces by morning. This feature should
interact with surface low/frontal boundary in eastern Montana to
initiate another round of deep convection. Currently there is some
capping however approaching wave should break cap with storms
becoming more organizing along Montana/Dakotas border this evening
propagating east overnight. Low level jet not all that impressive
at least from model solutions however enough instability and cape
with wave to likely keep storms going and could remain strong
later tonight into early Friday. Timing/coverage somewhat uncertain but
trends are impacts in our forecast area near or after midnight. With some
uncertainty did not increase probability of precipitation at this point. High res rapid
refresh model indicating potential of some stronger winds with
possible bowing complex reaching central Dakotas around 06z along
cold front. Slight risk area has been pushed far east as the
valley so storms will need to be monitored late tonight.
Front will push as far east as the valley on Friday middle day with
main precipitation threat lingering in the am. How far east will determine
where storms again could initiate in the afternoon. Far eastern
could be on the edge for storm development. Cold advection not
significant and surface westerly flow should allow temperatures to
recover close to average.
Looks quiet Friday night with forecast area in between frontal passages.
Long term...(saturday through thursday)
issued at 315 PM CDT Thursday Jul 24 2014
Next stronger cold front to drop through forecast area Saturday as upper low
sags into the northern forecast area. Air mass more stable with this boundary
so thunderstorms less of a threat. Best chance for showers will be
across the north as cold pool descends southward. With timing of
the front southeast half of the forecast area could still see maximum temperatures
close to average.
Secondary cold front drops through forecast area which will keep temperatures
well below average with some spotty rain showers along front.
Monday to Thursday...models in excellent agreement with 500mb northwest
flow aloft as western US under ridge and eastern US under the
trough. That gives the northern plains surface high pressure with
predominantly dry weather. Temperatures will trend from just below normal
to normal...with highs in the upper 70s to low 80s. Kept the isolated
pockets of slight chance for thunder Wednesday and Thursday as ridge attempts to
push east and here maybe a possibility of a wave able to ride ridge
and bring precipitation to the forecast area.
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 700 PM CDT Thursday Jul 24 2014
VFR conditions were across the area. Visible loop indicated cloud
decks moving east over eastern ND and far northern Minnesota. Ceilings have
lowered to around 35 hundred feet in the Devils Lake basin with precipitation
moving in. Ceilings over northern Minnesota was around 11 thousand feet. Elsewhere
MVFR ceilings appear to be developing over far southeast zones and