NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260921_0600
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)
=== ===== === ==== ==== === === === ====
Mon 09/21 06Z 0.11 0111  92  14   6 0.00
Mon 09/21 07Z 0.17 0113  90   7   6 0.00
Mon 09/21 08Z 0.20 0114  89   4   5 0.00
Mon 09/21 09Z 0.20 0116  87   2   5 0.00
Mon 09/21 10Z 0.20 0117  84   1   5 0.00
Mon 09/21 11Z 0.18 0117  84   1   5 0.00
Mon 09/21 12Z 0.17 0117  86   0   5 0.00
Mon 09/21 13Z 0.17 0116  88   1   4 0.00
Mon 09/21 14Z 0.16 0115  88   2   4 0.00
Mon 09/21 15Z 0.17 0114  88   2   4 0.00
Mon 09/21 16Z 0.17 0113  87   2   4 0.00
Mon 09/21 17Z 0.18 0112  84   2   4 0.00
Mon 09/21 18Z 0.18 0111  80   2   4 0.00
Mon 09/21 19Z 0.18 0210  77   2   4 0.00
Mon 09/21 20Z 0.14 0109  73   2   4 0.00
Mon 09/21 21Z 0.15 0210  68   2   5 0.00
Mon 09/21 22Z 0.14 0210  62   2   5 0.00
Mon 09/21 23Z 0.14 0210  56   2   5 0.00
Tue 09/22 00Z 0.15 0211  53   2   5 0.00
Tue 09/22 01Z 0.17 0311  49   2   5 0.00
Tue 09/22 02Z 0.15 0309  47   2   6 0.00
Tue 09/22 03Z 0.17 0409  45   2   5 0.00
Tue 09/22 04Z 0.18 0509  43   2   5 0.00
Tue 09/22 05Z 0.18 0608  43   2   5 0.00
Tue 09/22 06Z 0.17 0707  49   2   4 0.00
Tue 09/22 07Z 0.15 0806  55   2   4 0.00
Tue 09/22 08Z 0.13 1005  61   2   3 0.00
Tue 09/22 09Z 0.14 1106  62   2   3 0.00
Tue 09/22 10Z 0.13 1106  65   2   3 0.00
Tue 09/22 11Z 0.13 1206  69   2   2 0.00
Tue 09/22 12Z 0.13 1105  71   3   2 0.00
Tue 09/22 13Z 0.16 0906  71   3   2 0.00
Tue 09/22 14Z 0.17 0806  71   3   2 0.00
Tue 09/22 15Z 0.20 0606  70   3   2 0.00
Tue 09/22 16Z 0.28 0607  72   3   2 0.00
Tue 09/22 17Z 0.56 0606  74   3   2 0.00
Tue 09/22 18Z 1.19 0605  74   3   2 0.00
Tue 09/22 19Z 1.34 0505  76   3   2 0.00
Tue 09/22 20Z 1.43 0505  76   4   2 0.00
Tue 09/22 21Z 1.11 0606  77   4   2 0.00
Tue 09/22 22Z 0.73 0607  78   6   2 0.00
Tue 09/22 23Z 0.57 0608  77  10   2 0.00
Wed 09/23 00Z 0.58 0610  76  16   2 0.00
Wed 09/23 01Z 0.58 0611  73  22   2 0.00
Wed 09/23 02Z 0.58 0713  70  27   3 0.00
Wed 09/23 03Z 0.61 0814  65  29   3 0.00
Wed 09/23 04Z 0.54 0914  60  28   3 0.00
Wed 09/23 05Z 0.53 0916  57  22   3 0.00
Wed 09/23 06Z 0.48 0916  56  17   3 0.00
Wed 09/23 07Z 0.46 0917  50  11   4 0.00
Wed 09/23 08Z 0.43 0817  48   6   4 0.00
Wed 09/23 09Z 0.42 0816  45   5   4 0.00
Wed 09/23 10Z 0.42 0717  44   5   4 0.00
Wed 09/23 11Z 0.42 0816  46   6   4 0.00
Wed 09/23 12Z 0.43 0817  46   7   4 0.00
Wed 09/23 13Z 0.44 0818  48   7   4 0.00
Wed 09/23 14Z 0.43 0917  49   6   4 0.00
Wed 09/23 15Z 0.44 0916  50   6   4 0.00
Wed 09/23 16Z 0.42 0913  54   5   3 0.00
Wed 09/23 17Z 0.43 0911  54   4   3 0.00

Run total areal avg QPF for the Central_Greens is: 0.00 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