NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260209_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 02/09 06Z 0.12 3328  52  35 -12 0.00
Mon 02/09 07Z 0.14 3330  49  34 -11 0.00
Mon 02/09 08Z 0.13 3331  51  32 -11 0.00
Mon 02/09 09Z 0.12 3332  51  29 -11 0.00
Mon 02/09 10Z 0.10 3333  51  24 -11 0.00
Mon 02/09 11Z 0.09 3333  51  17 -11 0.00
Mon 02/09 12Z 0.10 3333  50  11 -11 0.00
Mon 02/09 13Z 0.08 3433  49   9 -11 0.00
Mon 02/09 14Z 0.07 3432  47  16 -11 0.00
Mon 02/09 15Z 0.07 3431  47  50 -11 0.00
Mon 02/09 16Z 0.08 3430  47  78 -11 0.00
Mon 02/09 17Z 0.09 3329  45  79 -11 0.00
Mon 02/09 18Z 0.09 3327  43  62 -11 0.00
Mon 02/09 19Z 0.10 3327  41  59 -10 0.00
Mon 02/09 20Z 0.12 3325  40  56 -10 0.00
Mon 02/09 21Z 0.12 3325  35  57  -9 0.00
Mon 02/09 22Z 0.11 3324  32  55  -9 0.00
Mon 02/09 23Z 0.10 3323  30  44  -9 0.00
Tue 02/10 00Z 0.10 3322  30  37  -8 0.00
Tue 02/10 01Z 0.11 3322  31  41  -8 0.00
Tue 02/10 02Z 0.11 3321  33  50  -8 0.00
Tue 02/10 03Z 0.11 3319  33  64  -8 0.00
Tue 02/10 04Z 0.09 3317  30  78  -8 0.00
Tue 02/10 05Z 0.10 3316  30  86  -8 0.00
Tue 02/10 06Z 0.10 3214  31  87  -8 0.00
Tue 02/10 07Z 0.13 3214  42  91  -8 0.00
Tue 02/10 08Z 0.14 3112  58  89  -8 0.00
Tue 02/10 09Z 0.14 3111  72  88  -8 0.00
Tue 02/10 10Z 0.15 3011  79  88  -7 0.00
Tue 02/10 11Z 0.16 3011  74  85  -6 0.00
Tue 02/10 12Z 0.14 2908  68  80  -6 0.00
Tue 02/10 13Z 0.13 2706  64  76  -6 0.00
Tue 02/10 14Z 0.13 2406  60  74  -6 0.00
Tue 02/10 15Z 0.15 2207  54  75  -6 0.00
Tue 02/10 16Z 0.19 2210  48  77  -6 0.00
Tue 02/10 17Z 0.20 2012  43  80  -7 0.00
Tue 02/10 18Z 0.17 1912  47  83  -7 0.00
Tue 02/10 19Z 0.04 1713  63  92  -6 0.00
Tue 02/10 20Z 0.04 1715  87  94  -5 0.00
Tue 02/10 21Z 0.03 1719  93  95  -5 0.03
Tue 02/10 22Z 0.06 1721  94  96  -5 0.07
Tue 02/10 23Z 0.12 1823  94  94  -6 0.09
Wed 02/11 00Z 0.23 1922  96  98  -7 0.06
Wed 02/11 01Z 0.29 2019  95  94  -8 0.06
Wed 02/11 02Z 0.33 2117  94  93  -8 0.06
Wed 02/11 03Z 0.37 2215  95  94  -8 0.05
Wed 02/11 04Z 0.42 2315  95  91  -8 0.04
Wed 02/11 05Z 0.43 2514  96  91  -8 0.03
Wed 02/11 06Z 0.46 2615  97  85  -8 0.02
Wed 02/11 07Z 0.50 2816  97  87  -8 0.01
Wed 02/11 08Z 0.50 2918  97  88  -9 0.01
Wed 02/11 09Z 0.44 3018  96  90 -10 0.01
Wed 02/11 10Z 0.39 3017  95  89 -10 0.01
Wed 02/11 11Z 0.34 3017  94  89 -11 0.01
Wed 02/11 12Z 0.30 3117  93  89 -11 0.01
Wed 02/11 13Z 0.26 3117  93  88 -11 0.01
Wed 02/11 14Z 0.25 3216  92  88 -12 0.00
Wed 02/11 15Z 0.28 3216  92  88 -12 0.00
Wed 02/11 16Z 0.29 3216  92  89 -12 0.00
Wed 02/11 17Z 0.28 3215  92  88 -12 0.00

Run total areal avg QPF for the Central_Greens is: 0.58 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