NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260606_1200
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)
=== ===== === ==== ==== === === === ====
Sat 06/06 12Z 0.37 2021  74  88  14 0.00
Sat 06/06 13Z 0.44 2121  75  88  14 0.01
Sat 06/06 14Z 0.52 2120  75  83  14 0.01
Sat 06/06 15Z 0.93 2220  81  96  13 0.01
Sat 06/06 16Z 1.46 2122  82  98  14 0.02
Sat 06/06 17Z 1.76 2125  82  94  14 0.03
Sat 06/06 18Z 1.72 2125  79  95  15 0.01
Sat 06/06 19Z 1.51 2226  90  93  15 0.15
Sat 06/06 20Z 0.80 2324  88  82  15 0.14
Sat 06/06 21Z 0.76 2225  90  75  15 0.03
Sat 06/06 22Z 0.74 2427  86  73  14 0.21
Sat 06/06 23Z 0.93 2428  88  69  14 0.01
Sun 06/07 00Z 1.10 2531  93  62  13 0.05
Sun 06/07 01Z 1.05 2530  94  75  12 0.02
Sun 06/07 02Z 1.09 2629  97  78  12 0.04
Sun 06/07 03Z 1.09 2629  97  80  11 0.05
Sun 06/07 04Z 1.01 2729  97  88  11 0.08
Sun 06/07 05Z 0.99 2729  97  89  11 0.10
Sun 06/07 06Z 0.96 2829  97  85  10 0.08
Sun 06/07 07Z 1.01 2831  98  78  10 0.06
Sun 06/07 08Z 1.03 2931  97  77  10 0.05
Sun 06/07 09Z 1.01 2931  97  72  10 0.04
Sun 06/07 10Z 1.00 2931  97  73   9 0.04
Sun 06/07 11Z 0.95 2931  97  71   9 0.06
Sun 06/07 12Z 0.93 2930  97  66   9 0.05
Sun 06/07 13Z 0.90 2928  97  62   9 0.05
Sun 06/07 14Z 0.87 3027  97  73   9 0.08
Sun 06/07 15Z 0.82 3126  98  80   8 0.09
Sun 06/07 16Z 0.64 3225  98  93   8 0.10
Sun 06/07 17Z 0.44 3326  98  95   8 0.11
Sun 06/07 18Z 0.39 3326  98  97   7 0.08
Sun 06/07 19Z 0.29 3427  98  97   7 0.04
Sun 06/07 20Z 0.21 3528  97  92   7 0.02
Sun 06/07 21Z 0.15 0026  95  65   7 0.01
Sun 06/07 22Z 0.12 0026  92  36   7 0.00
Sun 06/07 23Z 0.08 0027  87  20   7 0.00
Mon 06/08 00Z 0.17 0028  82  11   7 0.00
Mon 06/08 01Z 0.31 0130  75   3   6 0.00
Mon 06/08 02Z 0.53 0235  78   2   5 0.00
Mon 06/08 03Z 0.72 0237  72   1   5 0.00
Mon 06/08 04Z 0.74 0336  69   1   6 0.00
Mon 06/08 05Z 0.82 0436  68   0   6 0.00
Mon 06/08 06Z 0.83 0436  65   1   6 0.00
Mon 06/08 07Z 0.83 0435  63   1   6 0.00
Mon 06/08 08Z 0.80 0433  61   2   6 0.00
Mon 06/08 09Z 0.76 0431  59   2   6 0.00
Mon 06/08 10Z 0.69 0430  58   3   6 0.00
Mon 06/08 11Z 0.65 0429  56   4   6 0.00
Mon 06/08 12Z 0.59 0428  52   5   7 0.00
Mon 06/08 13Z 0.52 0424  51   5   7 0.00
Mon 06/08 14Z 0.47 0420  49   6   7 0.00
Mon 06/08 15Z 0.46 0416  50   7   7 0.00
Mon 06/08 16Z 0.71 0312  53   7   7 0.00
Mon 06/08 17Z 1.27 0208  56   7   7 0.00
Mon 06/08 18Z 0.52 0106  59   6   8 0.00
Mon 06/08 19Z 0.42 3505  64   6   8 0.00
Mon 06/08 20Z 0.32 3506  69   6   8 0.00
Mon 06/08 21Z 0.39 3306  74   7   8 0.00
Mon 06/08 22Z 0.25 3306  75   7   9 0.00
Mon 06/08 23Z 0.15 3307  71   7   9 0.00

Run total areal avg QPF for the greens is: 1.93 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