NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260917_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)
=== ===== === ==== ==== === === === ====
Thu 09/17 06Z 0.05 3203  98  18  12 0.00
Thu 09/17 07Z 0.04 3302  98  26  12 0.00
Thu 09/17 08Z 0.03 0400  98  38  12 0.00
Thu 09/17 09Z 0.04 1401  98  45  12 0.00
Thu 09/17 10Z 0.04 1503  98  43  11 0.00
Thu 09/17 11Z 0.04 1606  98  37  11 0.00
Thu 09/17 12Z 0.04 1709  98  32  11 0.01
Thu 09/17 13Z 0.09 1809  96  30  12 0.00
Thu 09/17 14Z 0.15 2009  95  44  12 0.00
Thu 09/17 15Z 0.20 2110  95  66  12 0.00
Thu 09/17 16Z 0.23 2210  95  84  12 0.00
Thu 09/17 17Z 0.25 2309  95  93  12 0.00
Thu 09/17 18Z 0.21 2208  92  92  13 0.00
Thu 09/17 19Z 0.22 2208  93  94  13 0.00
Thu 09/17 20Z 0.23 2209  96  97  13 0.00
Thu 09/17 21Z 0.23 2109  97  99  12 0.01
Thu 09/17 22Z 0.20 2107  99  99  12 0.03
Thu 09/17 23Z 0.11 2005  99  99  12 0.05
Fri 09/18 00Z 0.07 1806  99  99  12 0.10
Fri 09/18 01Z 0.11 1908  98  98  13 0.13
Fri 09/18 02Z 0.14 2008  99  95  13 0.08
Fri 09/18 03Z 0.24 2309 100  95  13 0.05
Fri 09/18 04Z 0.26 2810 100  97  13 0.04
Fri 09/18 05Z 0.24 3216  99  95  12 0.06
Fri 09/18 06Z 0.21 3220  95  95  12 0.03
Fri 09/18 07Z 0.25 3221  87  92  11 0.02
Fri 09/18 08Z 0.28 3221  75  75  11 0.00
Fri 09/18 09Z 0.28 3223  77  66  10 0.01
Fri 09/18 10Z 0.27 3223  77  43  10 0.01
Fri 09/18 11Z 0.24 3224  78  49   9 0.01
Fri 09/18 12Z 0.24 3225  80  37   8 0.01
Fri 09/18 13Z 0.23 3326  73  17   8 0.00
Fri 09/18 14Z 0.23 3325  72  13   7 0.00
Fri 09/18 15Z 0.42 3223  83  10   6 0.00
Fri 09/18 16Z 0.95 3222  81   5   6 0.00
Fri 09/18 17Z 1.20 3321  77   1   6 0.00
Fri 09/18 18Z 0.80 3319  71   1   5 0.00
Fri 09/18 19Z 1.00 3320  62   1   5 0.00
Fri 09/18 20Z 0.61 3319  57   1   5 0.00
Fri 09/18 21Z 0.26 3319  56   1   5 0.00
Fri 09/18 22Z 0.15 3319  53   1   5 0.00
Fri 09/18 23Z 0.13 3421  53   2   5 0.00
Sat 09/19 00Z 0.07 3422  51   2   5 0.00
Sat 09/19 01Z 0.05 3422  57   2   5 0.00
Sat 09/19 02Z 0.02 3522  59   2   4 0.00
Sat 09/19 03Z 0.05 3520  58   2   4 0.00
Sat 09/19 04Z 0.03 3519  54   2   5 0.00
Sat 09/19 05Z 0.04 3518  47   2   6 0.00
Sat 09/19 06Z 0.04 3517  42   3   6 0.00
Sat 09/19 07Z 0.03 3516  36   3   6 0.00
Sat 09/19 08Z 0.03 3515  32   3   6 0.00
Sat 09/19 09Z 0.05 3515  30   2   6 0.00
Sat 09/19 10Z 0.05 0013  30   2   6 0.00
Sat 09/19 11Z 0.06 0012  30   2   6 0.00
Sat 09/19 12Z 0.05 0010  30   2   5 0.00
Sat 09/19 13Z 0.04 0008  30   3   5 0.00
Sat 09/19 14Z 0.05 0007  32   3   5 0.00
Sat 09/19 15Z 0.03 0004  35   4   5 0.00
Sat 09/19 16Z 0.02 3504  39   4   5 0.00
Sat 09/19 17Z 0.02 3503  46   4   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.65 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