NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20241121_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 11/21 06Z 0.19 1517  90  55   3 0.00
Thu 11/21 07Z 0.24 1418  90  60   2 0.00
Thu 11/21 08Z 0.30 1318  91  65   2 0.01
Thu 11/21 09Z 0.35 1220  91  68   2 0.01
Thu 11/21 10Z 0.35 1220  91  68   2 0.01
Thu 11/21 11Z 0.35 1219  92  65   2 0.01
Thu 11/21 12Z 0.35 1219  93  71   2 0.01
Thu 11/21 13Z 0.36 1219  94  71   1 0.01
Thu 11/21 14Z 0.38 1219  95  74   1 0.01
Thu 11/21 15Z 0.41 1119  95  75   1 0.01
Thu 11/21 16Z 0.42 1118  96  78   1 0.01
Thu 11/21 17Z 0.44 1018  95  77   1 0.01
Thu 11/21 18Z 0.45 1018  95  81   1 0.01
Thu 11/21 19Z 0.47 0918  95  78   1 0.01
Thu 11/21 20Z 0.50 0918  96  83   0 0.01
Thu 11/21 21Z 0.53 0919  96  82   0 0.02
Thu 11/21 22Z 0.56 0820  96  80   0 0.03
Thu 11/21 23Z 0.59 0822  96  77   0 0.03
Fri 11/22 00Z 0.60 0923  95  81   0 0.04
Fri 11/22 01Z 0.60 0925  95  86   0 0.06
Fri 11/22 02Z 0.62 0926  95  88   0 0.08
Fri 11/22 03Z 0.65 0927  95  94   0 0.07
Fri 11/22 04Z 0.69 0828  95  93   0 0.05
Fri 11/22 05Z 0.73 0829  95  89   0 0.05
Fri 11/22 06Z 0.72 0829  95  92   0 0.04
Fri 11/22 07Z 0.77 0829  97  93   0 0.04
Fri 11/22 08Z 0.80 0830  97  94  -1 0.05
Fri 11/22 09Z 0.84 0832  97  94  -1 0.06
Fri 11/22 10Z 0.89 0833  97  94  -1 0.06
Fri 11/22 11Z 0.92 0834  97  92  -1 0.07
Fri 11/22 12Z 0.92 0835  97  88  -1 0.05
Fri 11/22 13Z 0.88 0935  97  78   0 0.04
Fri 11/22 14Z 0.86 0933  97  75   0 0.04
Fri 11/22 15Z 0.87 0932  97  66   0 0.05
Fri 11/22 16Z 0.87 0928  97  43  -1 0.03
Fri 11/22 17Z 0.86 1024  96  24  -1 0.02
Fri 11/22 18Z 0.94 1022  96  24  -2 0.01
Fri 11/22 19Z 0.93 1021  95  19  -2 0.01
Fri 11/22 20Z 0.87 1121  96  20  -2 0.01
Fri 11/22 21Z 0.75 1120  94  26  -2 0.01
Fri 11/22 22Z 0.71 1119  95  37  -2 0.01
Fri 11/22 23Z 0.64 1118  93  51  -2 0.01
Sat 11/23 00Z 0.60 1117  93  64  -2 0.01
Sat 11/23 01Z 0.57 1117  90  65  -2 0.01
Sat 11/23 02Z 0.56 1117  90  67  -2 0.01
Sat 11/23 03Z 0.58 1017  92  74  -2 0.01
Sat 11/23 04Z 0.46 1013  91  67  -2 0.00
Sat 11/23 05Z 0.31 0709  91  76  -2 0.00
Sat 11/23 06Z 0.22 0409  91  77  -1 0.01
Sat 11/23 07Z 0.17 0212  92  80  -2 0.01
Sat 11/23 08Z 0.12 0115  93  79  -2 0.01
Sat 11/23 09Z 0.05 0017  94  72  -2 0.00
Sat 11/23 10Z 0.09 3522  95  82  -2 0.00
Sat 11/23 11Z 0.09 0022  97  91  -2 0.02
Sat 11/23 12Z 0.10 3524  98  93  -3 0.04
Sat 11/23 13Z 0.14 3526  96  92  -2 0.03
Sat 11/23 14Z 0.17 3428  96  92  -2 0.02
Sat 11/23 15Z 0.21 3429  96  84  -2 0.02
Sat 11/23 16Z 0.20 3428  96  85  -2 0.02
Sat 11/23 17Z 0.29 3328  97  88  -2 0.03

Run total areal avg QPF for the greens is: 1.42 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