NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20241121_0600
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)
=== ===== === ==== ==== === === === ====
Thu 11/21 06Z 0.15 1416  88  69   2 0.00
Thu 11/21 07Z 0.20 1417  90  74   2 0.00
Thu 11/21 08Z 0.26 1318  90  79   2 0.01
Thu 11/21 09Z 0.31 1219  90  84   2 0.01
Thu 11/21 10Z 0.31 1219  90  80   2 0.01
Thu 11/21 11Z 0.31 1219  91  74   2 0.01
Thu 11/21 12Z 0.31 1219  94  84   1 0.01
Thu 11/21 13Z 0.35 1220  95  82   1 0.01
Thu 11/21 14Z 0.38 1121  96  86   1 0.01
Thu 11/21 15Z 0.43 1121  96  86   1 0.01
Thu 11/21 16Z 0.45 1121  97  91   1 0.01
Thu 11/21 17Z 0.47 1021  98  89   1 0.02
Thu 11/21 18Z 0.48 0921  97  89   1 0.02
Thu 11/21 19Z 0.48 0920  97  84   1 0.02
Thu 11/21 20Z 0.50 0920  98  89   0 0.02
Thu 11/21 21Z 0.52 0820  97  88   0 0.03
Thu 11/21 22Z 0.56 0821  97  88   0 0.04
Thu 11/21 23Z 0.61 0823  97  88   0 0.04
Fri 11/22 00Z 0.62 0923  97  91   0 0.05
Fri 11/22 01Z 0.61 0924  97  94   0 0.09
Fri 11/22 02Z 0.61 0925  97  95   0 0.11
Fri 11/22 03Z 0.66 0827  97  94   0 0.11
Fri 11/22 04Z 0.72 0828  97  94   0 0.08
Fri 11/22 05Z 0.76 0829  97  89   0 0.07
Fri 11/22 06Z 0.74 0828  97  91   0 0.06
Fri 11/22 07Z 0.79 0829  97  92   0 0.05
Fri 11/22 08Z 0.85 0830  97  92  -1 0.04
Fri 11/22 09Z 0.89 0832  97  93  -1 0.07
Fri 11/22 10Z 0.93 0834  97  93  -1 0.08
Fri 11/22 11Z 0.93 0834  98  90  -1 0.08
Fri 11/22 12Z 0.90 0835  97  84  -1 0.06
Fri 11/22 13Z 0.85 0934  97  70   0 0.05
Fri 11/22 14Z 0.83 0833  97  66   0 0.05
Fri 11/22 15Z 0.83 0930  98  53  -1 0.06
Fri 11/22 16Z 0.76 1025  98  31  -1 0.04
Fri 11/22 17Z 0.70 1121  97  19  -1 0.03
Fri 11/22 18Z 0.79 1120  97  22  -2 0.02
Fri 11/22 19Z 0.77 1119  95  20  -2 0.01
Fri 11/22 20Z 0.76 1119  96  21  -2 0.01
Fri 11/22 21Z 0.61 1219  94  27  -2 0.01
Fri 11/22 22Z 0.62 1119  95  40  -2 0.01
Fri 11/22 23Z 0.57 1118  92  57  -2 0.01
Sat 11/23 00Z 0.59 1117  94  65  -2 0.01
Sat 11/23 01Z 0.57 1117  90  65  -2 0.01
Sat 11/23 02Z 0.57 1017  90  71  -2 0.01
Sat 11/23 03Z 0.64 1018  95  75  -2 0.01
Sat 11/23 04Z 0.52 0914  95  74  -2 0.01
Sat 11/23 05Z 0.38 0711  95  89  -2 0.01
Sat 11/23 06Z 0.30 0411  95  86  -2 0.01
Sat 11/23 07Z 0.26 0214  95  83  -2 0.02
Sat 11/23 08Z 0.22 0118  95  81  -2 0.01
Sat 11/23 09Z 0.13 0019  95  75  -2 0.00
Sat 11/23 10Z 0.04 3522  96  82  -2 0.00
Sat 11/23 11Z 0.09 3523  97  91  -3 0.01
Sat 11/23 12Z 0.04 3525  98  93  -3 0.04
Sat 11/23 13Z 0.06 3426  97  91  -2 0.04
Sat 11/23 14Z 0.10 3430  96  92  -2 0.02
Sat 11/23 15Z 0.14 3432  96  83  -2 0.02
Sat 11/23 16Z 0.13 3430  96  85  -2 0.02
Sat 11/23 17Z 0.22 3330  97  85  -3 0.02

Run total areal avg QPF for the Central_Greens is: 1.80 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