Scientific Forecaster Discussion
fxus61 kbtv 230544
Area forecast discussion
National Weather Service Burlington Vermont
144 am EDT Fri Jun 23 2017
showers and thunderstorms will move through northern portions of
the area this morning, then area-wide later in the day. Locally
heavy rainfall is possible with stronger showers and storms. A
cold front will move through the region tonight, reducing the
humidity and bringing a brief return to dry weather is expected
on Saturday. More showers return early next week. Temperatures
will be near their seasonal normals, with highs in the 70s to
low 80s and lows in the 50s and low 60s.
Near term /through Friday night/...
as of 133 am EDT Friday...no changes with this update. Radar
showing precip has moved into the St. Lawrence Valley, and kmss
reporting light rain. Showers and rumble of thunder possible,
and timed for 3-4am arrival in the Champlain Valley and points
eastward. Ahead of that, quiet conditions will prevail with
increasing mid clouds and light winds leading to low temps
mainly in the 60s.
Previous discussion...retreating warm front brings shower
and thunderstorm activity back to the region this evening and
overnight. Carrying pretty high pops later this evening and the
remainder of the overnight. Strong warm advection bringing
moisture rich air back into the region very quickly. Precipitable water values
rapidly increase back into the 1.75-2.00" range with deep warm
cloud depths suggests heavy rainfall a possibility. Overall
progressive nature of the system with a big convective component
in the afternoon hours suggests areal risk of flash flooding
remains low in any given location so no watches at the moment.
Isolated flooding remains possible given very moist soil
Very challenging forecast for the daytime and evening hours
Friday. Kinematically speaking wind fields are favorable for
severe convection tomorrow. Deep layer shear in the 30-40 kt
range along with large sweeping low-level hodographs suggest
organized convection, including supercells. However, this is a
highly conditional risk given sufficient instability is able to
be realized. Morning shower activity, lots of low and mid-
level moisture would suggest that the sun will have a tough time
tomorrow developing any big cape. Despite good kinematic fields,
if there's no instability, organized convection will be limited,
and pulse marginal severe at best would be the result, along
with the heavy rainfall threat. If we see a lot of sun tomorrow
and develop any meaningful amounts of instability a higher end
severe threat would be expected. Will have to continue to
evaluate the stability parameters in the forecast through
tomorrow evening. Best shot at getting warm will be in the
Champlain Valley where downslope southwesterly flow off the
Adirondacks may help to clear out low level cloud cover. Have
mentioned gusty winds and heavy rainfall in the forecast and
hazardous weather outlook.
Short term /Saturday through Sunday/...
as of 300 PM EDT Thursday...mid/upper level trof will deepen
across the NE conus for the weekend with several embedded vorts.
Atmosphere will have much better dynamics to work with...but
moisture and stability profiles will be weaker than Friday...so
expecting less areal coverage of showers and embedded rumbles of
thunder. Neither Sat or sun will be a wash out...but will
continue to mention low chc pops between 18z-03z each aftn.
Instability ranges from 400 to 800 j/kg...with axis of highest
values near the international border each afternoon/evening with
strong mid/upper level westerly flow. Soundings show slightly
better instability with steeper lapse rates on Sunday aftn with
the potential for some localized gusty winds...but threat is
limited based on available energy. Progged 850mb temps btwn
10-12c Saturday support mainly 70s with values falling btwn 7-9c
on Sunday supporting highs mid 60s to l/M 70s warmer valleys.
Lows mainly in the upper 40s to mid/upper 50s over the weekend.
Depending upon areal coverage of precip...some patchy fog is
possible in the deeper protected valleys. Mid level moisture
associated with remnants of Cindy may produce a light shower
early Sat morning across extreme southern Rutland/Windsor
counties and have continued to mention low chc to cover this
Long term /Sunday night through Thursday/...
as of 300 PM EDT Thursday...large scale synoptic pattern shows
mid/upper level trof persisting across the Great Lakes into the
NE conus. This general setup will support at or below normal
temps with chances for showers...as unsettled weather is
expected. Thermal profiles show limited instability with some
afternoon heating producing daily cape values between 300-600
j/kg. A rumble or two of thunder is possible...especially when
the strong dynamics arrive during peak heating hours...but
overall severe threat is limited. Have tried to focus higher
pops during the aftn/evening hours...except on tues when better
dynamics and deeper moisture is present associated with
mid/upper level trof. Progged 850mb temps btwn 6-8c
Monday/Tuesday support highs in the mid 60s to lower 70s. These
low level thermal profiles slow warm back into the 9-11c by late
next week...supporting highs back into the mid 70s to lower
80s. Overnight lows range mainly in the mid 40s mountain valleys
to mid/upper 50s in the warmer urban areas of the Champlain
Aviation /06z Friday through Tuesday/...
through 06z Saturday...MVFR mainly in northern New York
terminals through morning with VFR cigs elsewhere. Scattered
rain shower/thunderstorm in kmss/kslk near issuance time will spread eastward
through 10z to the rest of the area as a warm front lifts north
across the forecast area. Went with prevailing rain shower and a tempo
group of thunderstorm early, then after passage of first batch of showers
have backed off to vcsh for the rest of the day. South to
soutwhest winds with gusts to 15-20 kts. Low level wind shear forecast 09-13z
kmss/kslk where low level jet will cause some shear until we get
daytime heating to mix things out.
Friday night: VFR. Chance MVFR rain showers...slight chance thunderstorms and rain.
Saturday: VFR. Chance rain showers.
Saturday night: VFR. Slight chance rain showers.
Sunday: VFR. Chance rain showers.
Sunday night: VFR. Chance rain showers.
Monday: VFR. Chance rain showers.
Monday night: VFR. Slight chance rain showers.
Tuesday: VFR. Chance rain showers.
an isolated flood threat on Friday. Last rainfall event
recharged streamflow across the region, and storms Friday will
be very efficient rainers given very high precipitable water values and some
possibility of training given the wind field. In addition some
heavy rainfall overnight tonight may saturate surface conditions
for Friday afternoon convection. Can't really pin down any one
location, and overall the system is pretty progressive so
widespread flash flooding is not expected at this time. Storm
total quantitative precipitation forecast of around an 1"-1.25" expected over central and
northern Vermont and northern New York...with lesser amounts to the south.
Don't anticipate any mainstem river flooding at this time.