NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260820_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)
=== ===== === ==== ==== === === === ====
Thu 08/20 00Z 1.07 2613  87  69  12 0.00
Thu 08/20 01Z 1.17 2615  86  67  12 0.00
Thu 08/20 02Z 0.78 2714  90  62  12 0.00
Thu 08/20 03Z 0.65 2715  94  61  12 0.01
Thu 08/20 04Z 0.58 2815  93  59  12 0.01
Thu 08/20 05Z 0.51 2814  91  49  12 0.01
Thu 08/20 06Z 0.51 2815  89  40  12 0.01
Thu 08/20 07Z 0.49 2915  88  29  11 0.00
Thu 08/20 08Z 0.48 2914  88  19  11 0.01
Thu 08/20 09Z 0.42 2913  86  30  11 0.00
Thu 08/20 10Z 0.39 2912  80  42  11 0.01
Thu 08/20 11Z 0.38 2911  74  28  11 0.01
Thu 08/20 12Z 0.37 2911  71  38  11 0.00
Thu 08/20 13Z 0.39 2911  69  46  10 0.00
Thu 08/20 14Z 0.40 2809  69  30  10 0.00
Thu 08/20 15Z 0.48 2708  67   8  10 0.00
Thu 08/20 16Z 1.03 2708  67   6  10 0.00
Thu 08/20 17Z 1.18 2707  69   6  10 0.00
Thu 08/20 18Z 1.35 2706  71   8  10 0.00
Thu 08/20 19Z 0.83 2705  72  10  10 0.00
Thu 08/20 20Z 0.63 2706  72   8  10 0.00
Thu 08/20 21Z 0.61 2708  75  11  10 0.00
Thu 08/20 22Z 0.45 2707  75  25  10 0.00
Thu 08/20 23Z 0.36 2706  75  20  10 0.00
Fri 08/21 00Z 0.29 2905  75  17  10 0.00
Fri 08/21 01Z 0.20 3105  75  16  10 0.00
Fri 08/21 02Z 0.13 3305  75  16  10 0.00
Fri 08/21 03Z 0.11 3504  74  15   9 0.00
Fri 08/21 04Z 0.13 0105  73  16   9 0.00
Fri 08/21 05Z 0.17 0206  74  16   9 0.00
Fri 08/21 06Z 0.21 0406  74  17   9 0.00
Fri 08/21 07Z 0.19 0405  73  16   9 0.00
Fri 08/21 08Z 0.18 0405  72  16   9 0.00
Fri 08/21 09Z 0.17 0405  72  15   9 0.00
Fri 08/21 10Z 0.18 0405  71  13   9 0.00
Fri 08/21 11Z 0.22 0505  71  13   9 0.00
Fri 08/21 12Z 0.27 0606  71  13   9 0.00
Fri 08/21 13Z 0.30 0607  72  12   9 0.00
Fri 08/21 14Z 0.44 0606  73  11   8 0.00
Fri 08/21 15Z 1.20 0605  75  11   9 0.00
Fri 08/21 16Z 2.17 0605  76   9   9 0.00
Fri 08/21 17Z 1.84 0503  75   7   9 0.00
Fri 08/21 18Z 1.63 0603  75   7  10 0.00
Fri 08/21 19Z 1.38 0703  75   6  10 0.00
Fri 08/21 20Z 0.87 0803  77   6  10 0.00
Fri 08/21 21Z 0.43 0802  80   6  10 0.00
Fri 08/21 22Z 0.25 0702  82   6  10 0.00
Fri 08/21 23Z 0.27 0803  82   7  10 0.00
Sat 08/22 00Z 0.33 0904  82   9  10 0.00
Sat 08/22 01Z 0.37 0905  82  10  10 0.00
Sat 08/22 02Z 0.41 1107  82  14  10 0.00
Sat 08/22 03Z 0.37 1207  83  16  10 0.00
Sat 08/22 04Z 0.28 1307  83  16  10 0.00
Sat 08/22 05Z 0.24 1408  82  17  10 0.00
Sat 08/22 06Z 0.21 1408  81  17  10 0.00
Sat 08/22 07Z 0.22 1307  80  18  10 0.00
Sat 08/22 08Z 0.23 1408  80  18  10 0.00
Sat 08/22 09Z 0.25 1408  80  17  10 0.00
Sat 08/22 10Z 0.26 1409  79  16   9 0.00
Sat 08/22 11Z 0.29 1310  79  14   9 0.00

Run total areal avg QPF for the greens is: 0.07 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