NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260916_0000
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)
=== ===== === ==== ==== === === === ====
Wed 09/16 00Z 0.08 1914  73  71  12 0.00
Wed 09/16 01Z 0.10 1916  70  82  12 0.00
Wed 09/16 02Z 0.17 1919  66  86  12 0.00
Wed 09/16 03Z 0.26 2022  63  89  12 0.00
Wed 09/16 04Z 0.32 2123  62  84  13 0.00
Wed 09/16 05Z 0.36 2223  63  79  13 0.00
Wed 09/16 06Z 0.45 2324  66  87  13 0.00
Wed 09/16 07Z 0.60 2427  70  90  12 0.00
Wed 09/16 08Z 0.57 2525  61  94  13 0.00
Wed 09/16 09Z 0.54 2622  72  92  13 0.00
Wed 09/16 10Z 0.50 2720  85  90  13 0.00
Wed 09/16 11Z 0.45 2819  93  79  13 0.01
Wed 09/16 12Z 0.41 2818  95  45  13 0.01
Wed 09/16 13Z 0.38 2916  97  36  13 0.01
Wed 09/16 14Z 0.36 2815  97  48  13 0.01
Wed 09/16 15Z 0.35 2814  96  61  13 0.01
Wed 09/16 16Z 0.34 2812  96  65  13 0.00
Wed 09/16 17Z 0.35 2712  95  70  13 0.00
Wed 09/16 18Z 0.35 2811  94  70  13 0.00
Wed 09/16 19Z 0.36 2811  94  68  13 0.00
Wed 09/16 20Z 0.35 2810  94  66  13 0.00
Wed 09/16 21Z 0.31 2910  94  60  13 0.00
Wed 09/16 22Z 0.29 2909  96  52  12 0.00
Wed 09/16 23Z 0.28 2909  95  39  12 0.00
Thu 09/17 00Z 0.24 2908  91  23  13 0.00
Thu 09/17 01Z 0.24 2909  90  14  13 0.00
Thu 09/17 02Z 0.20 3008  91  12  12 0.00
Thu 09/17 03Z 0.16 3006  92  11  12 0.00
Thu 09/17 04Z 0.13 3005  91  11  12 0.00
Thu 09/17 05Z 0.10 2803  92  12  12 0.01
Thu 09/17 06Z 0.09 2503  93  13  12 0.01
Thu 09/17 07Z 0.10 2304  95  17  12 0.01
Thu 09/17 08Z 0.11 2305  95  21  12 0.01
Thu 09/17 09Z 0.13 2306  96  24  12 0.01
Thu 09/17 10Z 0.14 2207  96  29  12 0.01
Thu 09/17 11Z 0.16 2208  95  38  12 0.00
Thu 09/17 12Z 0.17 2209  95  46  12 0.00
Thu 09/17 13Z 0.17 2209  96  46  12 0.01
Thu 09/17 14Z 0.17 2208  96  50  12 0.01
Thu 09/17 15Z 0.17 2209  97  55  12 0.01
Thu 09/17 16Z 0.18 2209  96  50  12 0.01
Thu 09/17 17Z 0.21 2210  95  60  12 0.01
Thu 09/17 18Z 0.26 2410  96  59  12 0.01
Thu 09/17 19Z 0.27 2510  94  49  12 0.01
Thu 09/17 20Z 0.26 2609  91  43  13 0.01
Thu 09/17 21Z 0.25 2709  87  40  13 0.00
Thu 09/17 22Z 0.25 2709  82  37  13 0.00
Thu 09/17 23Z 0.23 2809  78  44  13 0.00
Fri 09/18 00Z 0.23 2810  75  44  13 0.00
Fri 09/18 01Z 0.26 2811  74  38  13 0.01
Fri 09/18 02Z 0.27 2812  72  43  12 0.01
Fri 09/18 03Z 0.28 2913  64  50  12 0.01
Fri 09/18 04Z 0.28 2913  55  47  12 0.01
Fri 09/18 05Z 0.29 2914  50  48  12 0.01
Fri 09/18 06Z 0.31 3016  45  50  11 0.01
Fri 09/18 07Z 0.32 3018  45  56  10 0.01
Fri 09/18 08Z 0.35 3120  47  74   9 0.01
Fri 09/18 09Z 0.36 3122  50  68   9 0.01
Fri 09/18 10Z 0.41 3124  55  61   8 0.00
Fri 09/18 11Z 0.47 3126  71  35   7 0.00

Run total areal avg QPF for the greens is: 0.28 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