Area forecast discussion
National Weather Service Bismarck ND
1046 am CDT Sat may 18 2013
Update...
issued at 1024 am CDT Sat may 18 2013
The timing and location of convective initiation in this complex
scenario is the main focus today. Precipitation chances along the
Missouri River have generally been lowered for this morning and
early afternoon as low level stratus will help to stabilize the
atmosphere until the next middle level shortwave arrives this
afternoon.
The 12 and 13 UTC hrrr have picked up on the clearing over
northwestern South Dakota this morning...and now initiates
convection there and in southwestern North Dakota by 21 UTC. 12
UTC GFS thermodynamic profiles support this idea along with the 00
UTC European model (ecmwf) as cape is forecast to exceed 1000 j/kg there.
The current thinking is that convection will spread generally
east-northeastward until middle/late afternoon destabilization and
middle level height falls finally initiate additional convection
between the Missouri and James rivers along the Dakota border.
Update issued at 644 am CDT Sat may 18 2013
Update mainly for pop trends today. Showers and isolated storms
have pushed into the far northeast early this morning. Recent runs
of the rap have a good handle on near term trends...and have
reduced probability of precipitation through the morning into early afternoon. Still
expecting the focus of afternoon convection along a boundary to
the southeast...with potential for some severe storms to develop
by middle afternoon.
&&
Short term...(today and tonight)
issued at 430 am CDT Sat may 18 2013
The main focus in the short term is convective trends and
potential for severe weather this afternoon and tonight. In the
near term...the 18/07z rap model has a good handle on the location
of the current storms across the northeast half of the forecast
area. Storms should continue to lift north through the morning
hours. Afternoon redevelopment is expected to focus on the trough
extending across the southeast counties. Ml convective available potential energy around 1500 to
2000 j/kg are expected along with deep layer shear at or above 40
kts...sufficient for supercell development with large
hail/damaging wind threat. In the extreme southeast...low
lcl's...decent low level cape...and a narrow area of favorable
0-1km shear suggest there may also be a several hour window of
tornado threat through early evening.
The southeast half of the forecast area looks favored for the
heavier rainfall amounts through tonight. Significant rises on
mainstem rivers are not expected...but will be monitoring for
localized heavy runoff and isolated short term flooding due to
extreme rainfall rates or multiple rounds of storms.
Long term...(sunday through friday)
issued at 430 am CDT Sat may 18 2013
A large closed 500 mb low is forecast to drift through the region
Sunday through Tuesday. The threat for severe weather will
diminish during this period...but moderate to locally heavy rainfall
will persist. Additional rainfall amounts of 1 to 3 inches are
possible over the weekend through Tuesday...with the higher totals
toward the James River Valley. Again...significant responses are
not expected on area rivers...but will be watching smaller creeks
and streams...as well as the potential for urban flooding. Clouds
and rain will keep temperatures down in the 50s/lower 60s Monday and
Tuesday...before a warming trend from middle to late week.
&&
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1024 am CDT Sat may 18 2013
Low stratus has been very difficult to forecast this morning...but
should improve by 18 UTC. Showers and thunderstorms will cause
MVFR conditions at most taf sites today...with brief periods of
IFR possible in stronger storms. Fog and low stratus will likely
return after midnight tonight in the wake of precipitation.
&&
Bis watches/warnings/advisories...
none.
&&
$$
Update/aviation...scheck
short term/long term...rp Kinney
