Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
711 PM EDT Tuesday Mar 31 2015
A clear sky/VFR conditions this evening in advance of a weak low
pressure system. This system will provide a noted increase in middle
level cloud /5 to 8k feet/ from north to south throughout the night.
Greater prospects for light precipitation will remain north of the
all terminals. Diminishing gradient flow and moist near surface
conditions may promote some MVFR fog development during the early
morning hours. A limited coverage of lower VFR stratocumulus for
Wednesday as an increasingly dry/stable environment takes hold under
building high pressure.
//Dtw threshold probabilities...
* low for ceiling at or below 5000 feet prior to 06z...moderate potential
06z to 12z Wednesday morning.
Previous discussion...issued 323 PM EDT Tuesday Mar 31 2015
Short term... through tonight
Remaining rain and snow from this morning has since pushed off to
the east leaving behind persistent cloud cover over the entire County Warning Area.
These persistent clouds have just finally begun to diminish this
afternoon with northern areas seeing the diminishing trend already.
An area of vorticity will be in the process of shearing out and
moving off to the east by the time the next weak wave approaches the
northern County Warning Area overnight. This wave is much like the wave this
morning that brought snow to parts of the County Warning Area...however one big
difference is the amount of moisture. The lack of moisture with the
overnight wave will allow for the continuation of low chance probability of precipitation
already outlined in the grids. The only change will be to tighten
up the window of time that any precipitation will most likely fall. 12z
model runs have come in slightly drier...especially the NAM in
regards to precipitation across the northern half of the County Warning Area. With the
Saginaw Valley and thumb areas not warming up as much as southern
areas of Southeast Michigan...any precipitation is expected to stay all
snow as temperatures drop into the middle 20s for those areas. Areas
closer to the Ohio border are looking at hovering around the
freezing mark for overnight lows. Clouds will linger around through
the overnight hours as the next round clouds stream in from the next
wave currently moving across the northern Great Lakes. Once this
weak area of low pressure moves off to the east Wednesday
morning...clouds finally start to scatter out as upper level ridging
approaches the area.
Advancing strong middle-level ridge axis will strengthen surface high
pressure over the Ohio Valley on Wednesday, eventually forcing its
translation to the eastern Seaboard overnight. Rising heights
through the day signal a rebounding of the thermal field
characterized by 850 mb temperatures reaching 2-4c by late Wednesday evening.
Deep layer subsidence will favor mostly sunny skies aside from
passing high clouds and a partial coverage of diurnal stratocu.
Respectable insolation will, however, be offset by an augmentation of
the surface pressure field by the Great Lakes that will help sustain
an easterly component to the flow through the day. Expect the
gradient in high temperatures to range from middle 40s in The Thumb and
lake shadowed areas to middle 50s elsewhere...perhaps even approaching
60 in Washtenaw/Lenawee counties.
Deep layer southerly flow will organize and strengthen through
Wednesday night as height falls associated with the upper low
currently off the pacnw coast spread across the Front Range.
Temperatures off the deck will continue to rise overnight as 850 mb
temperatures rise to 10c by Thursday morning. Veering low-level flow
from southeast to south will allow temperatures to rise across at least the
western County Warning Area during the latter half of the night. However, continued
lake shadowing will suppress warming in the Detroit metropolitan area and
The Thumb. Once again expecting a noticeable gradient ranging from
lows around 45 closer to central lower Michigan and upper 30s east.
Furthermore, the local strengthening of the inversion and light
moisture transport off of the lakes introduce the Prospect for low
clouds to spread into the eastern County Warning Area Wednesday evening into
Strengthening warm front is forecast to be positioned over central
Ontario by Thursday morning, placing Southeast Michigan firmly in
the warm sector with a full day of warm advection and deep SW flow
expected. Convective remnants/debris associated with the previous
upstream convective cycle significantly increase uncertainty with
regard to forecasting the exact nature of the thermodynamic profile
on Thursday. However, warm air advection should be sufficient to force highs into
at least the middle/upper 60s while a relatively well-mixed scenario
transport the gradually increasing elevated wind field to the
surface, which supports the inherited forecast for gusts of 25 to 30
knots Thursday. The nature of prefrontal convection Thursday afternoon
is not easily diagnosed at this lead time. However, increasing
height falls and middle-level forcing will be superimposed on an
environment that will feature steepening lapse rates through the
day. A round of scattered showers or thunderstorms is certainly in
the offing for Thursday afternoon before cold frontal passage Ushers in cooler
The extended period looks to start off active as a low pressure
system moves northward into the Great Lakes region. The best chance
for precipitation on Friday will be in the southern part of the County Warning Area with a
better chance of rain in the north on Friday night. Temperatures are
expected to drop into the middle 30s on Friday night which could allow
some wet snowflakes to mix in with the rain. Uncertainty in the
timing and track of this system is quite low and therefore...have
only included chance probability of precipitation in the forecast for now. Dry conditions
are forecasted for Saturday as high pressure tries to nudge its way
into the Great Lakes region. Precipitation returns on Sunday as the next
system tracks across the area. Again models are in disagreement and
precipitation type and timing is uncertain. Have put in a rain snow mix for
early Sunday morning before changing into all rain for Sunday
afternoon before changing back to a rain and snow mix for Sunday
night and Monday.
High pressure in place tonight and Wednesday will provide light
winds and low waves. Southerly winds will increase Wednesday night
ahead of a cold front...which is expected to move through late
Thursday. Warm southerly flow will increase to 20 to 25 knots during
the day Thursday but stability will limit wind gust potential.
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).