Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
349 PM EDT Tuesday may 5 2015
Observational data including regional radar mosaic and water vapor
imagery shows the initial surge of large scale forcing and
widespread precipitation pushing eastward across the lower
peninsula. The back edge of this activity is now across far western
sections of lower Michigan. Linear extrapolation of reflectivity
supports this back edge to push across the County Warning Area in the 22-01z
timeframe. Been monitoring the southwest flank of the forcing over
portions of northern Indiana/northern Illinois for shower/tstorm
redevelopment. Nwp guidance has suggested it is development over
this area that will have a shot at tracking into far Southern Lower
Michigan between the same time period. A supprssed frontal boundary
well south of the state line limits the potential for thunder this
The question for tonight is then centered on the overall potential
for precipiation. Subsidence in the wake of this complex will
eventually lead to a period of precipation weakening. A loose model
consensus exists with the solution...with intra model continuity
even bouncing around a little bit. Large scale forcing will remain
fair...with 925-700mb deformation quite high in a zone across the
central County Warning Area. Large wavelength ridge amplification is expected to
take place which will lower tropospheric convergence to the
heightned deformation. As a result...expectations are for continued
rain shower chance during the overnight. Disagreement exists with
where exactly this stationary boundary will reside. Continue to
favor sections of the County Warning Area from the northern suburbs of Detroit/I 59
corridor northward to I 69. At the end of the period...ridge
amplification will begin to push the frontal zone northward as a
warm front. With the lack of uncertainty and lighter coverage of
rain/showers in hi-resolution models...lowered probability of precipitation into the chance
to likely category. The conditional aspect of tonight...does support
some locally higher quantitative precipitation forecast for those areas that see multiple rounds of
Long term...Wednesday through next Tuesday
The remnant middle level frontal boundary over Southeast Michigan will be lifted
northward to the Saginaw Valley and thumb by early Wednesday afternoon.
This will occur as a middle level ridge axis expands from the southern Ohio
Valley into the southern Great Lakes. The corresponding increase in middle
level subsidence will erode any residual middle level frontal
circulation and will lead to a decrease in lingering showers along
this front during the late morning into early afternoon. Diurnal
heating will also decrease the depth of the low level inversion and
will offer the opportunity for a decrease in the cloud cover during
the afternoon /especially across the southern half of the forecast area/.
Once clouds diminish...temperatures will quickly rise into the 70s /thicker
clouds across the Tri Cities and thumb may however keep these locals
in the 60s/. Model solutions develop some late day convection
associated with modest surface based instability from Adrian/Monroe into
SW lower Michigan along a remnant surface boundary. Model surface
dewpoints appear to be a little on the high side. Given this and
with a building middle level cap...nothing more than a slight chance of
late day convection appears warranted at this time.
The boundary layer will decouple Wednesday night with the middle level ridge
overhead and weak surface gradient in place. Both NAM and GFS suggest
surface dewpoints will hold in the 50s...leading to the potential for
some fog late Wednesday night/early Thursday morning. The middle level ridge
axis will push off to the east on Thursday while a short wave
impulse lifts across the northern plains. This will establish a low level
S-SW flow across Southeast Michigan on Thursday which will persist and actually
strengthen on Friday. This will advect a more Summer-like airmass
into Southeast Michigan...with highs likely surpassing the 80 degree mark. Both
GFS and European model (ecmwf) try to drive a weak surface boundary into lower Michigan Friday
afternoon. This and the potential for some weak short wave impulses
lifting into the area from the southwest and building instability
will support a chance of convection late Friday into Friday night.
Frontal boundary will continue to sag into the region Saturday as
continued shortwave energy embedded in upper swlys augment forcing
for ascent. 12z global models differ with their depiction of frontal
progression Saturday into early next week leading to relatively low
predictability in timing rounds of precipitation. For instance...12z GFS
pushes the front through the region late Saturday...while 12z European model (ecmwf)
basically stalls the front across lower Michigan. Former solution
would lead to a cooler/drier Sat night/Sunday and vice versa for the
latter. At this point will play middle of the Road with chance probability of precipitation
for the weekend /in collaboration with neighbors/ until better
predictability is shown by the model suite. Desert SW cutoff upper
low is forecast to open up and progress into the upper Midwest early
next week...warranting continued chances of showers/tstorms.
A weak gradient associated with high pressure over Lake Huron will
maintain light winds tonight right into Thursday. The high will then
drift to the east by the end of the weak and will open the door for
some light southerly winds late Thursday into Friday. And increase
in low level moisture late in the week into the weekend will also
pose the risk of some marine fog and the colder waters of Lake
Aviation...issued 154 PM EDT Tuesday may 5 2015
The mature mesoscale convective system and initial surge of deep moisture is currently
tracking through southeastern Michigan this afternoon. Latest data
suggests a continued potential for showers and thunderstorms over
much of the area through at least the early evening hours. A
developing warm front is then expected to slowly organize over
sections of semich tonight. Uncertainty exists to exactly where this
boundary will stall out for a time...but latest indications are
suggesting the northern Detroit metropolitan area through the I 69 corrdor.
It is along this boundary that a potential exists for
continued...long duration rain overnight. Focused this rain mention
at the kptk/kfnt for this taf issuance...will continue to monitor
the need for the southern taf sites. The other important issue for
tonight will be the potential for IFR/LIFR ceilings along and to the
south of the developing frontal boundary. Went more aggressive with
IFR/LIFR ceilings south.
For dtw...rain potential will now shift to more shower character as
the initial mature mesoscale convective system shifts northward through the County Warning Area. Will need
to monitor portions of northern Illinois/Indiana where additional
shower and thunderstorm development is forecasted to take place. It
remains possible this activity while moving eastward could impact
portions of far southern Michigan...including the metropolitan terminal.
Otherwise tonight...expectations at this time are for the warm front
to set up north of the terminal...focusing best long duration rains
chances north. LIFR ceilings tonight and tomorrow morning.
//Dtw threshold probabilities...
* high for ceiling below 5000 feet tonight.
* Low for thunderstorms this evening and tonight
* low for ceilings to fall below 200 feet.
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).