NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260927_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 09/27 18Z 0.61 0825  99  81   9 0.00
Sun 09/27 19Z 0.70 0828  98  72   9 0.03
Sun 09/27 20Z 0.76 0828  98  60   9 0.03
Sun 09/27 21Z 0.73 0828  98  50  10 0.03
Sun 09/27 22Z 0.71 0829  98  56  10 0.03
Sun 09/27 23Z 0.72 0830  97  63  10 0.03
Mon 09/28 00Z 0.68 0831  97  61  10 0.02
Mon 09/28 01Z 0.62 0931  97  70  11 0.02
Mon 09/28 02Z 0.59 0932  96  67  11 0.02
Mon 09/28 03Z 0.59 0932  96  60  11 0.01
Mon 09/28 04Z 0.58 0931  95  72  11 0.02
Mon 09/28 05Z 0.58 0931  96  86  11 0.02
Mon 09/28 06Z 0.56 0931  96  87  11 0.04
Mon 09/28 07Z 0.55 0930  96  81  11 0.02
Mon 09/28 08Z 0.50 0928  95  87  12 0.02
Mon 09/28 09Z 0.46 0926  94  78  12 0.01
Mon 09/28 10Z 0.43 0924  94  77  12 0.01
Mon 09/28 11Z 0.40 0922  95  79  12 0.01
Mon 09/28 12Z 0.38 0921  95  84  12 0.01
Mon 09/28 13Z 0.36 0920  96  84  12 0.01
Mon 09/28 14Z 0.35 0819  96  87  11 0.01
Mon 09/28 15Z 0.35 0818  97  91  11 0.01
Mon 09/28 16Z 0.35 0818  97  91  10 0.07
Mon 09/28 17Z 0.34 0717  98  90  10 0.05
Mon 09/28 18Z 0.33 0716  98  91   9 0.05
Mon 09/28 19Z 0.32 0714  98  92   8 0.03
Mon 09/28 20Z 0.30 0713  98  92   8 0.05
Mon 09/28 21Z 0.30 0713  98  85   8 0.05
Mon 09/28 22Z 0.30 0713  98  88   8 0.04
Mon 09/28 23Z 0.29 0713  97  95   9 0.03
Tue 09/29 00Z 0.29 0713  97  92   8 0.02
Tue 09/29 01Z 0.28 0713  97  92   8 0.01
Tue 09/29 02Z 0.25 0711  97  92   8 0.01
Tue 09/29 03Z 0.20 0709  97  92   8 0.00
Tue 09/29 04Z 0.15 0606  98  88   8 0.00
Tue 09/29 05Z 0.09 0404  98  91   7 0.00
Tue 09/29 06Z 0.08 0205  98  92   8 0.00
Tue 09/29 07Z 0.06 0107  98  93   8 0.00
Tue 09/29 08Z 0.06 0008  98  91   8 0.00
Tue 09/29 09Z 0.07 0009  97  86   8 0.00
Tue 09/29 10Z 0.11 0110  96  81   8 0.00
Tue 09/29 11Z 0.11 0110  95  80   8 0.00
Tue 09/29 12Z 0.11 0111  94  81   8 0.00
Tue 09/29 13Z 0.09 0110  95  84   8 0.00
Tue 09/29 14Z 0.06 0010  96  84   8 0.00
Tue 09/29 15Z 0.05 0010  97  87   8 0.00
Tue 09/29 16Z 0.05 3510  97  89   8 0.00
Tue 09/29 17Z 0.06 3511  97  85   8 0.00
Tue 09/29 18Z 0.08 0012  96  81   8 0.00
Tue 09/29 19Z 0.11 0013  95  77   8 0.00
Tue 09/29 20Z 0.13 0112  93  76   8 0.00
Tue 09/29 21Z 0.13 0111  93  75   8 0.00
Tue 09/29 22Z 0.10 0012  93  73   8 0.00
Tue 09/29 23Z 0.09 0013  89  73   9 0.00
Wed 09/30 00Z 0.09 0013  81  74   9 0.00
Wed 09/30 01Z 0.09 0012  72  73   9 0.00
Wed 09/30 02Z 0.11 0112  66  64   9 0.00
Wed 09/30 03Z 0.08 0010  61  49   9 0.00
Wed 09/30 04Z 0.06 0009  56  35  10 0.00
Wed 09/30 05Z 0.06 0007  47  22  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.82 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1