Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
353 PM EDT Monday Jul 6 2015
Short term...through tonight
High stability shown on kdtx radiosonde observation this morning...indicative of the
upper ridge still lingering over the area...will keep the weather
dry and quiet through the remainder of today. Cumulus field over western
Michigan has been expanding eastward this afternoon as southerly
flow has allowed for a slow but steady increase in moisture under an
inversion. Radar imagery over Wisconsin shows showers and
thunderstorms beginning to break out ahead of a cold front and ahead
of a strong upper shortwave that can be seen on water vapor imagery
tracking across Wisconsin. The strongest storms are firing just
ahead of the upper wave and where low-level Theta-E advection looks
the strongest per NAM/GFS. The upper shortwave will track through
northern Michigan this evening and overnight...spreading showers and
a few thunderstorms east. Consensus of the latest hi-res and global
models has been to speed up the arrival of precipitation
slightly...particularly over northern Michigan and Lake Huron. Newer
timing does look good...as models seem to have gotten a better
handle on the placement and strength of the upper wave over
Wisconsin...and with a low-level jet that will increase moisture and
elevated instability over lower Michigan later tonight. Expect
precipitation to spread into the area after midnight as deeper
moisture and instability arrive...with highest potential over the
Saginaw Valley towards sunrise. A few thunderstorms will also be
possible but expect overall coverage to be limited. Warmer air aloft
surging in with the low-level jet will keep activity (and
instability) elevated and even middle-level lapse rates are not all too
impressive. Severe weather is not anticipated.
Min temperatures will be on the warm side with increasing
clouds...rising dewpoints...and around 10 miles per hour of wind from the
south. Only expecting lows to fall into the middle 60s to near 70.
Long term... Tuesday through Sunday
Steady southeastward expansion of lower heights underway across the
northern plains this afternoon...prompted by a combination of a
stronger inbound wave entering North Dakota and a weaker impulse
lifting into southern Minnesota. The southern extent of these
height falls will continue eastward over the next 24 hours...
effectively shifting the attendant cold front across Southeast Michigan on
Tuesday. A period of deeper pre-frontal southwest flow will draw
the Reservoir of higher moisture existing just upstream /pw values
around 2 inches/ into the region late tonight and early Tuesday.
Diminishing stability as this process unfolds and with the onset of
daytime heating will provide a favorable background environment for
shower and thunderstorm development/maintenance as modest frontal
convergence translates through during the daylight period.
The overall potential for deeper convective growth and organization
appears limited. Main corridor of height falls and favorable
entrance region upper jet support will shift into southern Canada
during this time...leaving Southeast Michigan largely positioned south of
the greater middle level ascent and corresponding deep layer wind
field. In addition...residual warmer middle level temperatures and
questionable prospects for greater boundary layer destabilization
given an earlier frontal timing /centered 14z-18z/ will leave paltry
low and middle level lapse rates in place. 12z NAM again running high
on projected dewpoints /3-5 degrees too moist/...yielding an
overzealous early afternoon convective response. A more modified
parcel with a T/dew Point of 80/70 does allow for MLCAPE values within the
1000-1500 j/kg range. This could prove sufficient toward supporting
a few stronger updrafts...with a corresponding window for gusty
winds. Main issue given the high moisture content will be locally
Progressive Post-frontal drying late Tuesday into Tuesday evening
from northwest to southeast. This will lead in a brief period of
dry/stable conditions Tuesday night and Wednesday as high pressure
builds across the region. Highs Wednesday of lower and middle 70s
with noticeably lower humidity relative to Tuesday.
Middle level flow transitions to lower amplitude southwesterlies
immediately upstream of expanding subtropical ridging taking hold
over the southeast U.S. This evolution will potentially result in a
periodically active period through the latter half of the long term
period. This process will initiate Wednesday night and Thursday as
a lead wave ejects out of the growing upper height field across the
southern Continental U.S.. respectable surface wave appears to emerge with
this feature...resulting in a compact but strong corridor of forcing
and accompanying moisture transport that shifts into the Ohio
Valley/Great Lakes during this time. Exact timing and positioning
remains somewhat ill-defined yet...potential for at least northern
portions of Southeast Michigan to remain north of the eventual
precipitation swath. This continues to warrant a broader and more
conservative distribution of precipitation chances at this stage.
The extensive higher cloud and easterly low level gradient will cap
highs in the 70s Thursday...regardless of precipitation
Friday into next weekend...upper level anticyclone over the
southeastern US will expand north/westward. This looks to raise
heights locally to some degree leading to a modest warming trend.
This does not look to be a clean process though with the passage of
a few shortwaves in quasi-zonal flow allowing for precipitation chances to
continue through this period.
Moderate southerly flow tonight will shift to southwesterly Tuesday
as a cold front settles across the region. This front will bring a
good chance for showers and thunderstorms on Tuesday. Post-frontal
10 to 20 knot northwest winds develop late Tuesday and Tuesday
evening. Winds then diminish Tuesday night into early Wednesday as
high pressure builds across the region. A period of modest easterly
flow may develop as low pressure tracks through the Ohio Valley on
Aviation...issued 224 PM EDT Monday Jul 6 2015
Upper level high pressure will hold precipitation to our west until
Tuesday morning. Until then...high clouds...wildfire smoke...and
some cumulus filling in beneath an inversion near 4000 feet this
afternoon will be the only items of note. Area of showers developing
over Wisconsin will fill in as it moves towards the area tonight.
This should start to impact mbs with lower ceilings and rain showers
between 08 and 11z...and dtw between 12z and 15z.
Ceilings/visibilities in the area of rain showers is expected to be
low-end VFR or MVFR. Thunderstorms will also be possible...but
coverage is expected to be limited with early day timing and warmer
air aloft limiting instability.
//Dtw threshold probabilities...
* medium for ceilings below 4000 feet after 14z Tuesday.
* Low for thunderstorms after 14z Tuesday.
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).