Bermuda Weather Service Forecast Discussion

For Friday, February 28, 2020  21:00 UTC

FORECASTER - Alex Young 

Bermuda Weather Service Forecast Discussion
Friday 28th February, 2020, 2100UTC
Forecaster- Alex Young

NOWCAST: (This evening and tonight)
The day began fair with mainly mid-upper levels clouds as seen in 
satellite imagery. However, the clouds did not disperse as much as 
anticipated while a cold front moved further east away from our area. 
This resulted in a slightly lower max high of 20C/68F being recorded. 
An upper level low was seen over eastern provinces of Canada with 
a broad upper level trough digging through the US eastern states 
on WV imagery. Both the surface and upper levels have initialized 
fairly well with the global models synoptically and as such there 
is some confidence for the near term. All models suggest that a weak 
convergence band will pass over the island this evening bringing 
a few showers and will settle towards dawn. Conversely, global models 
continue to have a difficult time forecasting wind conditions as 
a weak ridge formed behind the passage of the front. Although, models 
all picked up the weak ridge and winds became light and variable 
throughout the day as forecast, the models struggle to have a consensus 
of the prevailing wind in the near term. As such there is lower confidence 
in winds during the early part of the evening before models align 
a bit better. Nonetheless, a light westerly wind possibly varying 
at times should back towards the southwest and increase to moderate 
overnight as another frontal system approaches from the northwest. 
Seas by the latest OPC chart have Bermuda south of the 9ft contour, 
which is consistent with model initialization of 7-8ft and as such 
there is high confidence that seas will remain moderate overnight. 


Warning Strategy: No warnings are required for the period.

AVIATION:
Runway 30 expected to be the active runway for the night as a light 
westerly wind eventually settles to a moderate south-westerly overnight. 
Mostly VFR conditions expected during the period, though there is 
the low chance of a few developing showers bringing brief MVFR conditions 
and/or a wet runway during the evening. For more information visit: 
http://weather.bm/aviation/

SHORT TERM FORECAST (Saturday through Sunday)
The upper trough moves off the US eastern coastline Saturday and 
hangs around into Sunday though though not really supporting the 
development of the frontal system. This is because a positively tilted 
jet core remains well east of this trough, with the right front quadrant 
well to our east. As such a rather weak cold front is expected to 
pass overnight on Saturday with occasional light to moderate showers 
beginning from Saturday afternoon. Models also consistently predict 
a secondary trough developing behind the front which passes early 
Sunday afternoon. Between the front and trough QPF values are not 
impressive going for about 0.5-0.75 of rainfall over both days with 
the GFS being the highest of the three global models.  Though the 
front is weak, a mass of colder air follows behind it with gradual 
cooling occurring behind the front as 850mb temperatures reaches 
near 0C by Sunday morning with the 540dm thickness line just to our 
north. This rush of cold air and the secondary trough will maintain 
cloudy skies and lingering showers into Sunday afternoon before they 
are forecast to ease. The wind surge linked to this developing frontal 
system differs slightly on all global solutions and as such a blend 
of the global models was utilized. Current projections indicate a 
moderate to strong west-southwesterly wind regime during the day 
on Saturday which veers westerly overnight. The wind then veers west-northwesterly 
after the secondary trough passes early Sunday afternoon and increases 
to strong and to a peak near 30 knots by both the GFS and UK, before 
decreasing back to moderate overnight. A few fluctuations in wind 
strength are anticipated, however, its difficult to say when exactly 
these will occur with certainty. Otherwise, seas will rapidly build 
to rough on Saturday and possibly become very rough on Sunday before 
slowly abating from late night. 

Warning Strategy: A small craft warning is effect through Saturday 
through Sunday morning and will need to be extended to cover the 
remainder of Sunday. An airfield warning will be needed for the periods; 
mainly Saturday late morning to early evening and Sunday morning 
through evening.

LONG TERM FORECAST (Monday through Tuesday)
A broad upper level ridge approaches from the west by Monday while 
high pressure builds in from the west at the surface. This multi-layered 
ridge will bring a return to drier and more stable conditions, though 
some lingering cloud will exist early on Monday. Winds and seas continue 
to decrease on Monday in response to the high pressure. In addition, 
with the center of the high forecast to pass overnight on Monday 
by all global models, winds will likely become light and variable. 
This coupled with clear skies will aid radiational cooling and a 
cooler nighttime temperature. Winds will then settle southerly moderate 
later on Tuesday. Seas remain rough for most of Monday, but finally 
return to a moderate state sometime late night on Monday or possibly 
very early on Tuesday.

Warning Strategy: A small craft warning will most likely be needed 
for most of the period on Monday.