NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260920_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)
=== ===== === ==== ==== === === === ====
Sun 09/20 12Z 0.28 2018  95  98   6 0.00
Sun 09/20 13Z 0.23 1919  95  99   6 0.02
Sun 09/20 14Z 0.20 1920  97  99   7 0.04
Sun 09/20 15Z 0.17 1821  97  99   7 0.07
Sun 09/20 16Z 0.16 1821  98  99   8 0.06
Sun 09/20 17Z 0.21 1923  98  99   8 0.09
Sun 09/20 18Z 0.25 1924  98  99   8 0.09
Sun 09/20 19Z 0.29 2024  98  99   8 0.10
Sun 09/20 20Z 0.30 2021  99  99   8 0.10
Sun 09/20 21Z 0.30 2117  99  98   8 0.09
Sun 09/20 22Z 0.27 2312  99  98   8 0.06
Sun 09/20 23Z 0.19 2608  99  80   8 0.02
Mon 09/21 00Z 0.12 3107  99  61   8 0.01
Mon 09/21 01Z 0.04 3410  98  48   8 0.00
Mon 09/21 02Z 0.02 3411  91  46   8 0.00
Mon 09/21 03Z 0.03 3513  79  46   8 0.00
Mon 09/21 04Z 0.05 3515  71  27   8 0.00
Mon 09/21 05Z 0.06 3516  64   9   7 0.00
Mon 09/21 06Z 0.08 3519  65   2   7 0.00
Mon 09/21 07Z 0.08 3520  75   1   6 0.00
Mon 09/21 08Z 0.09 3520  80   1   6 0.00
Mon 09/21 09Z 0.07 3520  83   1   5 0.00
Mon 09/21 10Z 0.05 3519  82   2   5 0.00
Mon 09/21 11Z 0.08 3520  83   2   4 0.00
Mon 09/21 12Z 0.11 0020  82   1   4 0.00
Mon 09/21 13Z 0.09 0019  78   1   4 0.00
Mon 09/21 14Z 0.10 0017  71   2   5 0.00
Mon 09/21 15Z 0.09 0017  67   2   5 0.00
Mon 09/21 16Z 0.13 0116  63   2   5 0.00
Mon 09/21 17Z 0.14 0115  59   1   5 0.00
Mon 09/21 18Z 0.16 0115  56   1   5 0.00
Mon 09/21 19Z 0.18 0214  55   1   5 0.00
Mon 09/21 20Z 0.17 0114  52   1   5 0.00
Mon 09/21 21Z 0.18 0214  50   1   5 0.00
Mon 09/21 22Z 0.19 0215  48   1   5 0.00
Mon 09/21 23Z 0.21 0216  48   2   5 0.00
Tue 09/22 00Z 0.23 0217  49   2   5 0.00
Tue 09/22 01Z 0.26 0318  49   2   6 0.00
Tue 09/22 02Z 0.27 0416  48   2   6 0.00
Tue 09/22 03Z 0.28 0515  47   2   5 0.00
Tue 09/22 04Z 0.24 0512  47   2   5 0.00
Tue 09/22 05Z 0.22 0610  49   2   5 0.00
Tue 09/22 06Z 0.21 0709  49   2   4 0.00
Tue 09/22 07Z 0.19 0908  51   2   4 0.00
Tue 09/22 08Z 0.19 0908  53   2   3 0.00
Tue 09/22 09Z 0.17 1007  56   2   3 0.00
Tue 09/22 10Z 0.16 1006  57   2   3 0.00
Tue 09/22 11Z 0.17 0906  57   2   2 0.00
Tue 09/22 12Z 0.15 0706  56   2   3 0.00
Tue 09/22 13Z 0.17 0607  54   2   3 0.00
Tue 09/22 14Z 0.15 0506  54   3   3 0.00
Tue 09/22 15Z 0.19 0507  54   3   3 0.00
Tue 09/22 16Z 0.22 0507  56   3   3 0.00
Tue 09/22 17Z 0.31 0407  60   3   2 0.00
Tue 09/22 18Z 0.84 0507  63   4   2 0.00
Tue 09/22 19Z 1.06 0506  65   4   2 0.00
Tue 09/22 20Z 1.34 0506  68   5   2 0.00
Tue 09/22 21Z 1.52 0607  72   5   2 0.00
Tue 09/22 22Z 0.89 0609  73   6   2 0.00
Tue 09/22 23Z 0.79 0611  71   7   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.75 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