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_0000
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 00Z 0.09 3104  92  21  13 0.00
Thu 09/17 01Z 0.08 3104  91  16  13 0.00
Thu 09/17 02Z 0.06 3305  92  15  13 0.00
Thu 09/17 03Z 0.05 3304  93  15  13 0.00
Thu 09/17 04Z 0.05 3203  95  18  13 0.00
Thu 09/17 05Z 0.06 3002  96  20  13 0.00
Thu 09/17 06Z 0.04 2901  97  25  12 0.00
Thu 09/17 07Z 0.04 2300  97  26  12 0.00
Thu 09/17 08Z 0.05 2002  98  34  12 0.00
Thu 09/17 09Z 0.06 2003  98  41  12 0.00
Thu 09/17 10Z 0.08 2005  98  39  12 0.00
Thu 09/17 11Z 0.11 2005  98  40  12 0.00
Thu 09/17 12Z 0.11 2006  98  39  12 0.01
Thu 09/17 13Z 0.14 2107  98  40  12 0.00
Thu 09/17 14Z 0.16 2107  98  44  12 0.00
Thu 09/17 15Z 0.20 2208  98  50  12 0.00
Thu 09/17 16Z 0.23 2308  98  62  13 0.00
Thu 09/17 17Z 0.22 2308  99  80  13 0.01
Thu 09/17 18Z 0.20 2208  99  91  13 0.02
Thu 09/17 19Z 0.21 2208  99  95  13 0.03
Thu 09/17 20Z 0.24 2309 100  97  13 0.05
Thu 09/17 21Z 0.23 2508 100  98  13 0.06
Thu 09/17 22Z 0.17 2806  98  98  13 0.07
Thu 09/17 23Z 0.14 2906  96  99  13 0.10
Fri 09/18 00Z 0.12 3006  93  97  13 0.07
Fri 09/18 01Z 0.10 3105  87  92  14 0.04
Fri 09/18 02Z 0.12 3006  87  88  13 0.00
Fri 09/18 03Z 0.15 3007  90  86  13 0.00
Fri 09/18 04Z 0.18 3009  92  84  12 0.00
Fri 09/18 05Z 0.20 3010  91  92  12 0.01
Fri 09/18 06Z 0.21 3112  89  85  12 0.01
Fri 09/18 07Z 0.28 3015  89  81  11 0.01
Fri 09/18 08Z 0.28 3118  87  69  11 0.01
Fri 09/18 09Z 0.27 3119  76  60  11 0.01
Fri 09/18 10Z 0.26 3221  69  48  10 0.01
Fri 09/18 11Z 0.26 3224  77  46   9 0.01
Fri 09/18 12Z 0.25 3325  86  27   8 0.01
Fri 09/18 13Z 0.27 3325  84  10   7 0.00
Fri 09/18 14Z 0.28 3324  81  17   7 0.00
Fri 09/18 15Z 0.62 3322  85  15   6 0.00
Fri 09/18 16Z 1.73 3322  82   7   6 0.00
Fri 09/18 17Z 2.51 3320  79   1   5 0.00
Fri 09/18 18Z 3.17 3221  78   2   5 0.00
Fri 09/18 19Z 1.99 3220  72   2   5 0.00
Fri 09/18 20Z 1.08 3320  68   2   5 0.00
Fri 09/18 21Z 0.39 3320  59   1   5 0.00
Fri 09/18 22Z 0.16 3321  49   2   6 0.00
Fri 09/18 23Z 0.10 3421  45   2   6 0.00
Sat 09/19 00Z 0.06 3422  47   3   6 0.00
Sat 09/19 01Z 0.05 3423  52   3   5 0.00
Sat 09/19 02Z 0.02 3423  56   3   5 0.00
Sat 09/19 03Z 0.05 3521  56   4   5 0.00
Sat 09/19 04Z 0.08 3521  56   4   5 0.00
Sat 09/19 05Z 0.07 3519  56   6   4 0.00
Sat 09/19 06Z 0.07 3518  53   7   5 0.00
Sat 09/19 07Z 0.07 0017  47   7   5 0.00
Sat 09/19 08Z 0.06 3516  41   7   5 0.00
Sat 09/19 09Z 0.03 3514  36   7   5 0.00
Sat 09/19 10Z 0.03 3514  31   7   6 0.00
Sat 09/19 11Z 0.02 3514  28   7   6 0.00

Run total areal avg QPF for the Central_Greens is: 0.54 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