NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260330_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 03/30 06Z 0.80 2228  51  69   0 0.00
Mon 03/30 07Z 0.83 2230  55  53   1 0.00
Mon 03/30 08Z 0.80 2333  58  39   1 0.00
Mon 03/30 09Z 0.76 2333  58  23   2 0.00
Mon 03/30 10Z 0.76 2433  57  13   2 0.00
Mon 03/30 11Z 0.77 2433  58   3   2 0.00
Mon 03/30 12Z 0.79 2433  58  27   2 0.00
Mon 03/30 13Z 0.83 2533  58  48   2 0.00
Mon 03/30 14Z 0.89 2533  58  55   1 0.00
Mon 03/30 15Z 0.96 2532  55  45   2 0.00
Mon 03/30 16Z 1.04 2530  55  57   2 0.00
Mon 03/30 17Z 1.25 2529  59  76   3 0.00
Mon 03/30 18Z 1.54 2430  64  73   3 0.00
Mon 03/30 19Z 3.15 2431  68  67   3 0.00
Mon 03/30 20Z 2.83 2531  72  67   4 0.00
Mon 03/30 21Z 3.39 2531  70  73   4 0.00
Mon 03/30 22Z 3.12 2531  68  77   3 0.00
Mon 03/30 23Z 2.04 2632  75  86   3 0.00
Tue 03/31 00Z 1.48 2632  79  87   3 0.03
Tue 03/31 01Z 1.18 2632  87  87   4 0.05
Tue 03/31 02Z 1.16 2630  90  84   4 0.04
Tue 03/31 03Z 1.10 2627  91  79   4 0.02
Tue 03/31 04Z 1.01 2625  93  76   4 0.01
Tue 03/31 05Z 0.84 2623  95  62   4 0.02
Tue 03/31 06Z 0.64 2621  96  59   4 0.03
Tue 03/31 07Z 0.46 2616  96  90   4 0.03
Tue 03/31 08Z 0.27 2610  95  97   5 0.03
Tue 03/31 09Z 0.18 2208  97  97   5 0.03
Tue 03/31 10Z 0.19 2013  99  84   5 0.02
Tue 03/31 11Z 0.28 2017  99  92   6 0.03
Tue 03/31 12Z 0.36 2122  98  94   7 0.09
Tue 03/31 13Z 0.42 2124  98  99   7 0.10
Tue 03/31 14Z 0.66 2330  99  98   7 0.24
Tue 03/31 15Z 0.69 2427  99  98   7 0.10
Tue 03/31 16Z 0.68 2428  99  96   8 0.11
Tue 03/31 17Z 0.70 2529  99  92   8 0.08
Tue 03/31 18Z 0.61 2625  99  83   8 0.04
Tue 03/31 19Z 0.54 2522  99  82   8 0.03
Tue 03/31 20Z 0.51 2421 100  80   8 0.05
Tue 03/31 21Z 0.47 2520  99  75   9 0.04
Tue 03/31 22Z 0.43 2320  99  73   9 0.08
Tue 03/31 23Z 0.43 2221  99  88   9 0.09
Wed 04/01 00Z 0.38 2221  99  86   9 0.10
Wed 04/01 01Z 0.37 2320  98  96   9 0.34
Wed 04/01 02Z 0.40 2419  97  96   8 0.41
Wed 04/01 03Z 0.30 2316  99  98   9 0.17
Wed 04/01 04Z 0.33 2419  99  90   8 0.12
Wed 04/01 05Z 0.37 2519  97  84   8 0.04
Wed 04/01 06Z 0.45 2521  99  55   7 0.01
Wed 04/01 07Z 0.56 2623  98  49   7 0.02
Wed 04/01 08Z 0.61 2626  97  49   8 0.01
Wed 04/01 09Z 0.60 2626  97  62   8 0.01
Wed 04/01 10Z 0.58 2626  97  87   8 0.05
Wed 04/01 11Z 0.53 2524  99  79   8 0.03
Wed 04/01 12Z 0.51 2525  99  97   8 0.08
Wed 04/01 13Z 0.40 2520  99  93   8 0.05
Wed 04/01 14Z 0.32 2718  99  73   7 0.04
Wed 04/01 15Z 0.26 2816  99  55   7 0.02
Wed 04/01 16Z 0.23 2916  99  49   6 0.01
Wed 04/01 17Z 0.20 3016  98  66   6 0.01

Run total areal avg QPF for the Central_Greens is: 2.91 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