NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260820_1200
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 08/20 12Z 0.33 2909  86  57  11 0.00
Thu 08/20 13Z 0.37 2810  84  42  11 0.00
Thu 08/20 14Z 0.39 2808  85  27  11 0.00
Thu 08/20 15Z 0.42 2808  81  19  11 0.00
Thu 08/20 16Z 0.59 2807  75  18  11 0.00
Thu 08/20 17Z 0.82 2806  71  19  11 0.00
Thu 08/20 18Z 0.82 2806  69  24  11 0.00
Thu 08/20 19Z 0.87 2906  73  19  11 0.00
Thu 08/20 20Z 0.43 2907  78  20  11 0.00
Thu 08/20 21Z 0.22 3006  81  30  11 0.01
Thu 08/20 22Z 0.17 3004  80  32  11 0.01
Thu 08/20 23Z 0.10 3204  80  19  11 0.00
Fri 08/21 00Z 0.08 3203  80  32  11 0.01
Fri 08/21 01Z 0.08 3304  80  33  10 0.01
Fri 08/21 02Z 0.11 3505  81  26  10 0.01
Fri 08/21 03Z 0.11 0006  81  28  10 0.00
Fri 08/21 04Z 0.12 0008  78  26  10 0.00
Fri 08/21 05Z 0.16 0109  74  23   9 0.00
Fri 08/21 06Z 0.21 0110  68  19   9 0.00
Fri 08/21 07Z 0.24 0111  64  18   9 0.00
Fri 08/21 08Z 0.21 0110  61  17   9 0.00
Fri 08/21 09Z 0.22 0210  60  17   9 0.00
Fri 08/21 10Z 0.26 0309  60  17   9 0.00
Fri 08/21 11Z 0.31 0410  60  19   9 0.00
Fri 08/21 12Z 0.34 0510  60  21   9 0.00
Fri 08/21 13Z 0.36 0510  60  20   9 0.00
Fri 08/21 14Z 0.38 0609  63  16   9 0.00
Fri 08/21 15Z 0.50 0607  67  14   9 0.00
Fri 08/21 16Z 1.34 0606  70  13   9 0.00
Fri 08/21 17Z 2.34 0505  72  10   9 0.00
Fri 08/21 18Z 2.13 0504  73   9  10 0.00
Fri 08/21 19Z 1.43 0604  75   8  10 0.00
Fri 08/21 20Z 1.12 0604  77   8  10 0.00
Fri 08/21 21Z 0.92 0604  77   8  10 0.00
Fri 08/21 22Z 0.73 0604  79   7  10 0.00
Fri 08/21 23Z 0.60 0605  80   7  10 0.00
Sat 08/22 00Z 0.72 0707  80   7  10 0.00
Sat 08/22 01Z 0.67 0808  80   8  10 0.00
Sat 08/22 02Z 0.67 0909  80   8   9 0.00
Sat 08/22 03Z 0.57 1009  81   9   9 0.00
Sat 08/22 04Z 0.47 1010  80  10   9 0.00
Sat 08/22 05Z 0.41 1110  78  10   9 0.00
Sat 08/22 06Z 0.41 1110  76  11   9 0.00
Sat 08/22 07Z 0.44 1010  77  11   9 0.00
Sat 08/22 08Z 0.47 1011  79  11   9 0.00
Sat 08/22 09Z 0.47 1012  79  12   9 0.00
Sat 08/22 10Z 0.49 1013  79  13   9 0.00
Sat 08/22 11Z 0.51 1015  79  15   9 0.00
Sat 08/22 12Z 0.49 1116  79  18   9 0.00
Sat 08/22 13Z 0.47 1116  80  20  10 0.00
Sat 08/22 14Z 0.45 1116  81  21  10 0.00
Sat 08/22 15Z 0.45 1114  83  22  10 0.00
Sat 08/22 16Z 0.49 1112  85  24  10 0.00
Sat 08/22 17Z 0.48 1110  85  25  10 0.00
Sat 08/22 18Z 0.42 1209  85  26  11 0.00
Sat 08/22 19Z 0.34 1110  84  25  11 0.00
Sat 08/22 20Z 0.30 1110  84  25  11 0.00
Sat 08/22 21Z 0.27 1211  86  25  11 0.00
Sat 08/22 22Z 0.27 1212  87  27  12 0.00
Sat 08/22 23Z 0.25 1213  89  27  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.05 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