NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260816_1800
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)
=== ===== === ==== ==== === === === ====
Sun 08/16 18Z 0.34 1906  85  12  12 0.00
Sun 08/16 19Z 0.45 1907  85  13  12 0.00
Sun 08/16 20Z 0.31 1909  86  20  12 0.01
Sun 08/16 21Z 0.24 1911  84  20  13 0.00
Sun 08/16 22Z 0.14 1812  84  25  13 0.00
Sun 08/16 23Z 0.10 1814  90  73  13 0.00
Mon 08/17 00Z 0.18 1918  94  85  13 0.02
Mon 08/17 01Z 0.33 2022  96  92  13 0.03
Mon 08/17 02Z 0.42 2026  97  91  13 0.03
Mon 08/17 03Z 0.46 2129  98  85  13 0.03
Mon 08/17 04Z 0.49 2128  98  84  13 0.03
Mon 08/17 05Z 0.50 2129  98  86  13 0.02
Mon 08/17 06Z 0.48 2129  98  89  13 0.02
Mon 08/17 07Z 0.47 2228  97  90  14 0.02
Mon 08/17 08Z 0.50 2228  97  92  14 0.01
Mon 08/17 09Z 0.47 2225  98  92  14 0.02
Mon 08/17 10Z 0.43 2223  98  93  14 0.02
Mon 08/17 11Z 0.43 2321  98  93  14 0.02
Mon 08/17 12Z 0.41 2319  98  91  14 0.02
Mon 08/17 13Z 0.36 2316  98  91  14 0.02
Mon 08/17 14Z 0.31 2313  98  89  14 0.02
Mon 08/17 15Z 0.24 2310  98  89  15 0.01
Mon 08/17 16Z 0.23 2309  98  92  15 0.02
Mon 08/17 17Z 0.25 2309  98  91  14 0.02
Mon 08/17 18Z 0.22 2507  98  85  14 0.01
Mon 08/17 19Z 0.18 2605  98  81  15 0.01
Mon 08/17 20Z 0.16 2804  97  68  15 0.00
Mon 08/17 21Z 0.15 3005  97  64  14 0.00
Mon 08/17 22Z 0.11 3205  96  42  15 0.00
Mon 08/17 23Z 0.11 3206  94  25  15 0.00
Tue 08/18 00Z 0.08 3307  94  25  14 0.00
Tue 08/18 01Z 0.07 3408  95  26  14 0.01
Tue 08/18 02Z 0.05 3509  94  17  14 0.01
Tue 08/18 03Z 0.05 3508  94  13  14 0.01
Tue 08/18 04Z 0.05 0008  94  24  13 0.01
Tue 08/18 05Z 0.06 0008  94  19  13 0.01
Tue 08/18 06Z 0.06 0008  93   9  13 0.01
Tue 08/18 07Z 0.05 0008  91   5  13 0.00
Tue 08/18 08Z 0.04 0007  88   4  13 0.00
Tue 08/18 09Z 0.04 3507  85   2  13 0.00
Tue 08/18 10Z 0.03 3506  83   2  13 0.00
Tue 08/18 11Z 0.03 3506  81   2  13 0.00
Tue 08/18 12Z 0.03 3506  79   2  13 0.00
Tue 08/18 13Z 0.02 0005  77   2  13 0.00
Tue 08/18 14Z 0.02 3504  78   2  12 0.00
Tue 08/18 15Z 0.03 3403  78   2  12 0.00
Tue 08/18 16Z 0.07 3203  80   2  12 0.00
Tue 08/18 17Z 0.06 3303  79   2  12 0.00
Tue 08/18 18Z 0.06 3203  79   2  12 0.00
Tue 08/18 19Z 0.12 3104  78   3  12 0.00
Tue 08/18 20Z 0.15 3005  75   3  12 0.00
Tue 08/18 21Z 0.19 3006  73   3  12 0.00
Tue 08/18 22Z 0.23 3007  72   3  12 0.00
Tue 08/18 23Z 0.20 3007  73   4  12 0.00
Wed 08/19 00Z 0.20 3107  77   4  12 0.00
Wed 08/19 01Z 0.20 3108  80   4  12 0.00
Wed 08/19 02Z 0.16 3007  81   5  12 0.00
Wed 08/19 03Z 0.17 2907  81   6  12 0.00
Wed 08/19 04Z 0.19 2907  80   8  12 0.00
Wed 08/19 05Z 0.20 2908  79  10  12 0.00

Run total areal avg QPF for the greens is: 0.47 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