(meteorobs) Weather Prospects for the Transit of Venus - VIIi

[Skywayinc at aol.com]

       The northern cold front that we've been concerned about for the past 
week will apparently never get much farther south than the Canadian/New England 
border; apparently it will push north as a warm front during Monday night . . 
. widely scattered diurnal-type thunderstorms may pop-up during Monday 
afternoon across northern New England and upstate New York.   

I've just taken a gander at the new 00Z run of the ETA model.

       As noted earlier . . . on the ETA, moisture in three levels of the 
atmosphere are depicted.  For 8 a.m. on Tuesday, the middle and upper levels (R2 
and R3) of the atmosphere are still forecast to be quite dry across much of 
the Northeast US, the Great Lakes States and Ohio Valley.  However, the lowest 
level -- the R1 -- is forecast to be very moist.  

       The R1 level depicts that part of the atmosphere between 1000 and 965 
mbs . . . or roughly between sea level and 1,500-feet.  

That is where most observers will likely be on Tuesday morning!  

       It has been my experience, that once the relative humidity in the R1 
level exceeds 80%, that scuddy low-level cloudiness tends to be prevailent.  
Obviously, the higher the humidity level, the thicker and more extensive is the 
cloudiness.  This type of cloudiness usually burns off/thins out as the Sun 
climbs higher into the sky.  

       The good news is that the projected humidity values from the new ETA 
run for the R1 layer have dropped by an average of 5 to 10% for many of the 20 
cities that I had listed earlier.  The biggest drops were in Dayton, Ohio 
(15%) and Philadelphia (13%).  This may be a signal that the low-level cloudiness, 
may not be quite as thick or widespread as had been earlier suggested.

       Below are the updated relative humidity values for the R1 level for 20 
selected cities off of the latest 00Z run of ETA FOUS output.  Next to each 
value is the difference in percent compared to the previous ETA run of Sunday 
afternoon.  Once again, above the R1 level (above 1,500-feet) , the R2 and R3 
levels have humidity values that are only about half as much!  

Location                               RH for R1 level    Difference from 12Z 
Sun.
--------------                             ----------------------             
--------------
Albany                                          80%                        -6
Burlington                                      78%                       +2
Boston                                          76%                        -4
Philadelphia                                   83%                      -13
Williamsport                                   92%                       -5
New York (La Guardia)                    83%                       -9
Portland, ME.                                 80%                       -7
Caribou                                          79%                       -7
Bangor                                           83%                       -7
Concord                                         76%                       -2
Bufallo                                           74%                      +1
Pittsburgh                                      78%                      +2
Cleveland                                       69%                       -8
Dayton                                           79%                     -15
Indianapolis                                    88%                       -4
Charleston, WV                              71%                      +1
Washington, DC                             92%                       -5
Norfolk                                           95%                      +4
Detroit                                            82%                      
-7
Chicago                                         81%                       +2  
       

So, while low cloudiness is still a bit of an issue for many localities, it 
might not be quite as bad as had earlier been thought.

I hope to issue one final outlook sometime late in the day on Monday 
("Transit Eve").
      
-- joe rao

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