Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
320 am EDT Sat Aug 2 2014
Short term...today and tonight
Middle level cold pool over the western Great Lakes...as 00z grb radiosonde observation
checked in with a 500 mb of -16 c. The upper level trough axis
will be slowly advancing east today...moving overhead during the
peak heating cycle...and another day of scattered showers and
thunderstorms is expected. MLCAPES look to be solid 2000
j/kg...with modest moisture pooling as indicated by 850-700 mb
Theta-E fields lining up over Southeast Michigan. With moderate
instability and favorable freezing levels...will allow for the
possibility of isolated severe hail. Fortunately...wind fields
remain anemic at surface and even at 500 mb. Slow motion of the cells
could produce some heavy rainfall...with precipitable water values around 1 inch.
As far as maxes go today...looking at comparable temperatures to
yesterday or slightly cooler ... 850 mb temperatures forecasted to come
up just short of 14 c...which is what the 00z DTX sounding revealed.
Finally look to be getting height rises/upper level shortwave riding
building into the central Great Lakes tonight...but that could set
the stage for some fog with 1020 mb surface high strung across the
area...especially if convective activity during the day deposits
substantial rainfall. With favorable radiating night should see mins
in the middle 50s to lower 60s.
Long term...Sunday through Friday
Broad upper level trough will remain anchored over the area into
early to middle next week as additional shortwave energy digs south and
east into the northern Great Lakes and maintain trough axis very
near the region. This will mean a continuation of the pattern the
area has experienced late in the week as temperatures climb to 80
degrees...give or take a degree and isolated to scattered showers
and thunderstorms develop within instability associated with the
modest upper level cool pool associated with this upper trough.
With the notable shortwave digging from central Canada into the
Great Lakes...precipitation chances will increase in the Monday and
Tuesday time frame after little more than isolated afternoon/evening
showers/storms on Sunday due to lack of any significant upper level
support or low level forcing. This approaching shortwave will aid in
both of these deficiencies heading into early next week.
The upper level pattern then undergoes a bit of a transition late in
the forecast period as a strong zonal push off of the northern
Pacific leads to a progressive pattern which at least temporarily
shunts mean upper trough east/northeast of the region. As this more
zonal northern stream pattern overspreads Canada...a significant
shortwave is still forecast by medium range models to meander east
within weaker southern stream and possibly encroach on the region by
late in the week. Confidence in the evolution of this system remains
very low given the complexity of the pattern change and questions
regarding the degree of interaction between the southern/northern
stream in such a scenario. Given fact that this wave seems to be
trapped south/southwest of shortwave ridge as it rolls over into
area with expansion of zonal jet stream across Canada...it still
seems reasonable to assume the eastward progress of this system will
be sluggish and will go no higher than chance probability of precipitation during the last
half of next week.
A surface high pressure system over the central Great Lakes will
produce a weak wind field with wind speeds remaining at 10 knots or
less through the weekend...resulting in minimal wave heights. Widely
scattered showers/thunderstorms will be possible despite this high
pressure...but will favor land areas as lake breeze boundaries
provide the primary focus during the afternoon and early evening
hours. Shower and thunderstorm chances will increase slightly into
early next week as additional shortwave energy digs into the area
and provides better focus for convection.
Aviation...issued 1200 am EDT Sat Aug 2 2014
Pockets of thicker middle level cloud will filter through overnight...
but skies will remain clear below 5k feet as nocturnal stability
increases. Light winds may promote a brief period of patchy light
fog with some minor visibility restrictions 09z-12z. There will be a
chance for shower and thunderstorm development again Saturday
afternoon...greatest potential in ptk and dtw/yip.
//Dtw threshold threats...
* low confidence in ceilings below 5000 feet on Saturday.
* Low confidence in thunderstorm potential Saturday afternoon.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).