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More than Cold Enough 850 Temps and 1000-500 Thicknesses


vortex95

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This morning at 06z, BOS had a 527 1000-500 thickness, it was

-4 C at 850 mb with a NW sfc and boundary layer wind, diurnal

minimum for sfc temp, and *still* the precip was all rain.  Same 
deal all the way out to 495.  Obviously mild enough in the lowest
1000 ft for complete melting to occur.  Boundary layer temp at BOS 
was 2 C.  Just goes to show that the empirical rules don't always work.
I would have thought the diurnal minimum would have been more
than enough for snow b/c you remove the sun this time of year, and 
it is often a completely different story for ptype.  We lacked precip 
intensity, and it was quite shallow.  At 06z it was raining at home and
the full moon was very much visible though the thin overcast, so not
really any good deep layer vertical motion to mix down the colder air
from above to get snow.  
Is CoastalWx reading this?  :underthewx:
 
I recall one time in March,1990 I believe, it was 65 F at 00z with
scattered tstms in ern MA, and 8 hours later it was heavy snow with
4-8" total.  It's always good to actually see the limits pushed/verified in
the real world!
 
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This morning at 06z, BOS had a 527 1000-500 thickness, it was

-4 C at 850 mb with a NW sfc and boundary layer wind, diurnal

minimum for sfc temp, and *still* the precip was all rain.  Same 
deal all the way out to 495.  Obviously mild enough in the lowest
1000 ft for complete melting to occur.  Boundary layer temp at BOS 
was 2 C.  Just goes to show that the empirical rules don't always work.
I would have thought the diurnal minimum would have been more
than enough for snow b/c you remove the sun this time of year, and 
it is often a completely different story for ptype.  We lacked precip 
intensity, and it was quite shallow.  At 06z it was raining at home and
the full moon was very much visible though the thin overcast, so not
really any good deep layer vertical motion to mix down the colder air
from above to get snow.  
Is CoastalWx reading this?  :underthewx:
 
I recall one time in March,1990 I believe, it was 65 F at 00z with
scattered tstms in ern MA, and 8 hours later it was heavy snow with
4-8" total.  It's always good to actually see the limits pushed/verified in
the real world!

 

 

Two words:  Partial thickness...

 

The lowest partial thickness interval was annihilated by diabatic heating yesterday.  It's in part what I have been discussing recently about how this time of year normalizes the thermal fields.

 

The precipiation fall rates were not intense enough to overcome the resulting lower 1300'.  The heated ground combined with cloud ceiling arriving at sunset was a radiation barrier -- it's pretty predictable actually.  In fact, it rained all the way to Caribou Maine yesterday;  I even posted the obs, suggesting it might be difficult to snow given the environmental conditions.  

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Don't know why anyone would expect anything other then rain with the cool air drainage source region being out of the Canadian Maritime's its been a stale garbage air mass for well over a week now here, And no snow pack to speak of for the air to flow over

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