Area forecast discussion
National Weather Service Bismarck ND
123 am CDT sun may 19 2013
Update...
issued at 117 am CDT sun may 19 2013
Updated forecast to remove the Severe Thunderstorm Watch for the
south central. Also made considerable changes to probability of precipitation this morning
based on latest radar and near term guidance. This resulted in
removing probability of precipitation north where radar shows no precipitation...and
keeping higher probability of precipitation south where radar shows rain and isolated
thunderstorms with models maintaining this activity.
Update issued at 824 PM CDT Sat may 18 2013
Severe Thunderstorm Watch continues until 1 am CDT Sunday for
south central North Dakota and portions of southwest North Dakota.
Latest radar imagery shows a large are of moderate to heavy
showers and thunderstorms...isolated severe with large hail and
heavy rainfall the main threats thus far. This is essentially
occurring from near Tuttle...southwest to prairie nights resort.
Watching thunderstorms upstream in South Dakota for potential
Hydro issues later tonight as more heavy rain is forecast to
advance into southeast North Dakota. Still have thunderstorms in
eastern Montana and far western North Dakota...but might scale
back the Severe Thunderstorm Watch in the next couple of hours
across portions of the southwest.
Update issued at 554 PM CDT Sat may 18 2013
A Severe Thunderstorm Watch has been issued for most of south
central and portions of southwestern North Dakota. Monitoring
radar and this will be the focus through the evening.
&&
Short term...(this evening through sunday)
issued at 302 PM CDT Sat may 18 2013
The main focus this afternoon is on the potential for severe
thunderstorms through tonight.
Low level convergence stretching from Dickinson to the Black Hills
has proven to be sufficient to break the cap this afternoon. Visible
satellite indicates some agitated cumulus there...and at least one
thunderstorm has been warned there. Based on anvil blow
off...there will probably be only limited surface heating into
northwestern South Dakota...so it appears that the best chance for
severe will hold off at least a few more hours until middle level
height falls spread into the central Dakotas atop better
instability and more favorable shear than that currently over
southwestern North Dakota. This is supported by the shower that
formed around 19 UTC and failed to gain steam near Hettinger.
Using visible satellite and radar...it appears that the most
likely scenario is for convection to slowly spread into
southwestern North Dakota over the next 5 hours...then move
eastward. These storms should then propagate east-northeastward
into southeastern North Dakota...with the best chance for severe
weather being along and south of I-94.
Thereafter...lingering showers and thunderstorms are forecast
through the weekend as broad low pressure is cut off over the
northern plains.
Long term...(sunday night through saturday)
issued at 302 PM CDT Sat may 18 2013
The main forecast highlight of the extended period will be
precipitation chances and amounts Sunday night through late
Tuesday.
There is still some disagreement amongst the 12z deterministic
models regarding the placement and movement of the h500 closed upper
level low over the northern plains. The 12z GFS keeps the h500 low a
bit faster and further south than the gefs/ecwmf/Gem Monday and
Tuesday...which introduces some differences in the timing and
placement of precipitation across North Dakota early in the
extended. As a consequence have kept chance/likely probability of precipitation through middle
Tuesday before bringing down probability of precipitation from northwest to southeast as the
h500 low slowly drifts east and away from the northern plains. For
quantitative precipitation forecast...have used a blend of model guidance as well as the wpc
guidance for amounts...which has an additional 1 to 2 inches of
rainfall from Sunday evening through late Tuesday for locations
south of State Highway 2. To the north (including the Souris river
basin)...up to an inch of additional rainfall is possible. As said
with previous forecast issuances...significant responses are not
expected on area rivers...but will be watching smaller creeks and
streams...as well as the potential for urban flooding.
Beyond Wednesday...the ecwmf and GFS solutions diverge with the
placement and movement of the next western Continental U.S. Upper level
trough...however...there is agreement that an upper level ridge will
begin to build over the central US as the aforementioned closed low
departs east. A slow warming trend through the end of this coming
week and clearing skies Thursday are expected across North Dakota.
&&
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 117 am CDT sun may 19 2013
IFR and lower stratus and areas of fog will develop over all
terminals early this morning and persist through at least 14-15z.
Kisn-kmot look to scatter out to MVFR later Sunday morning...while
the south maintains low ceilings near IFR. Kjms will continue to
experience scattered thunderstorms through at least 09z. Moderate
to heavy bands of rain and isolated thunderstorms also expected
Sunday and Sunday night most areas.
&&
Bis watches/warnings/advisories...
none.
&&
$$
Update...New Hampshire
short term...jws
long term...lth
aviation...New Hampshire
