Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260309_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)
=== ===== === ==== ==== === === === ====
Mon 03/09 12Z 0.75 2429  55  41   4 0.00
Mon 03/09 13Z 0.78 2431  47  33   5 0.00
Mon 03/09 14Z 0.76 2432  39  30   5 0.00
Mon 03/09 15Z 0.74 2332  38  28   6 0.00
Mon 03/09 16Z 0.78 2332  35  27   6 0.00
Mon 03/09 17Z 0.85 2233  31  28   6 0.00
Mon 03/09 18Z 0.93 2233  27  28   6 0.00
Mon 03/09 19Z 0.91 2232  26  26   6 0.00
Mon 03/09 21Z 0.84 2331  29  23   7 0.00
Mon 03/09 23Z 0.88 2433  37  34   7 0.00
Tue 03/10 00Z 0.91 2434  40  39   7 0.00
Tue 03/10 01Z 0.94 2434  42  41   7 0.00
Tue 03/10 02Z 0.92 2433  42  44   7 0.00
Tue 03/10 04Z 0.91 2534  43  48   7 0.00
Tue 03/10 05Z 0.91 2634  44  51   7 0.00
Tue 03/10 06Z 0.89 2632  47  49   7 0.00
Tue 03/10 07Z 0.87 2731  52  47   6 0.00
Tue 03/10 09Z 0.69 2725  61  50   7 0.00
Tue 03/10 10Z 0.60 2722  64  53   7 0.00
Tue 03/10 11Z 0.51 2620  64  50   7 0.00
Tue 03/10 12Z 0.46 2518  64  46   8 0.00
Tue 03/10 13Z 0.48 2519  69  35   7 0.00
Tue 03/10 14Z 0.50 2420  73  42   7 0.00
Tue 03/10 15Z 0.53 2421  76  31   7 0.00
Tue 03/10 16Z 0.59 2422  78  32   7 0.00
Tue 03/10 17Z 0.63 2421  81  43   7 0.00
Tue 03/10 18Z 0.69 2421  85  49   6 0.00
Tue 03/10 19Z 0.66 2519  88  49   7 0.00
Tue 03/10 20Z 0.71 2519  91  49   7 0.00
Tue 03/10 21Z 0.74 2620  94  47   6 0.00
Tue 03/10 22Z 0.71 2620  96  44   6 0.00
Tue 03/10 23Z 0.58 2718  97  46   6 0.00
Wed 03/11 00Z 0.47 2817  98  49   6 0.00
Wed 03/11 01Z 0.31 2913  99  51   5 0.01
Wed 03/11 02Z 0.21 3010  99  50   5 0.02
Wed 03/11 03Z 0.15 3008  99  50   5 0.02
Wed 03/11 04Z 0.11 3006  99  54   4 0.02
Wed 03/11 05Z 0.11 3006  98  48   4 0.02
Wed 03/11 06Z 0.08 2804  96  56   5 0.02
Wed 03/11 07Z 0.05 2502  95  55   5 0.01
Wed 03/11 08Z 0.02 1803  94  60   5 0.01
Wed 03/11 09Z 0.02 1609  96  81   6 0.01
Wed 03/11 10Z 0.04 1614  98  86   6 0.00
Wed 03/11 11Z 0.07 1520  98  87   7 0.00
Wed 03/11 12Z 0.09 1526  97  82   7 0.00
Wed 03/11 13Z 0.07 1631  97  71   7 0.00
Wed 03/11 14Z 0.04 1634  97  55   8 0.01
Wed 03/11 15Z 0.05 1737  97  46   8 0.02
Wed 03/11 16Z 0.09 1737  96  51   8 0.04
Wed 03/11 17Z 0.13 1838  96  59   9 0.03
Wed 03/11 18Z 0.17 1837  98  76  10 0.03
Wed 03/11 19Z 0.21 1937  98  69  10 0.02
Wed 03/11 20Z 0.28 1938  98  62  10 0.02
Wed 03/11 21Z 0.28 1938  98  50  10 0.03
Wed 03/11 22Z 0.31 2039  98  86  10 0.02
Wed 03/11 23Z 0.35 2041  98  84  10 0.02

Run total areal avg QPF for the Central_Greens is: 0.38 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