NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260928_1800
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 09/28 18Z 0.20 0807 100  95   9 0.00
Mon 09/28 19Z 0.22 0808  99  93   9 0.01
Mon 09/28 20Z 0.22 0708  99  93   8 0.01
Mon 09/28 21Z 0.24 0708  99  93   8 0.02
Mon 09/28 22Z 0.21 0608  99  92   8 0.02
Mon 09/28 23Z 0.19 0508  99  91   8 0.01
Tue 09/29 00Z 0.14 0407  98  89   9 0.01
Tue 09/29 01Z 0.13 0308  97  91   9 0.00
Tue 09/29 02Z 0.13 0308  97  91   9 0.00
Tue 09/29 03Z 0.12 0208  98  95   9 0.00
Tue 09/29 04Z 0.09 0107  97  97   9 0.01
Tue 09/29 05Z 0.04 0008  97  96  10 0.00
Tue 09/29 06Z 0.03 3509  97  94  10 0.00
Tue 09/29 07Z 0.04 3510  97  93  10 0.00
Tue 09/29 08Z 0.05 0011  96  92  10 0.00
Tue 09/29 09Z 0.04 3511  95  91  10 0.00
Tue 09/29 10Z 0.04 3512  95  88  10 0.00
Tue 09/29 11Z 0.04 3512  95  89  10 0.00
Tue 09/29 12Z 0.06 3512  95  87  10 0.00
Tue 09/29 13Z 0.06 0012  96  85  10 0.00
Tue 09/29 14Z 0.08 0012  96  83  10 0.00
Tue 09/29 15Z 0.07 0012  97  84  10 0.00
Tue 09/29 16Z 0.06 0012  97  86   9 0.00
Tue 09/29 17Z 0.06 0012  97  85   9 0.00
Tue 09/29 18Z 0.06 0011  96  84   9 0.00
Tue 09/29 19Z 0.06 0011  95  81  10 0.00
Tue 09/29 20Z 0.07 0010  93  75  10 0.00
Tue 09/29 21Z 0.08 0109  92  69  10 0.00
Tue 09/29 22Z 0.06 0010  93  66  10 0.00
Tue 09/29 23Z 0.06 0009  93  61  10 0.00
Wed 09/30 00Z 0.05 0009  93  54  10 0.00
Wed 09/30 01Z 0.03 3508  94  50   9 0.00
Wed 09/30 02Z 0.02 3507  93  47  10 0.00
Wed 09/30 03Z 0.02 3507  92  42  10 0.00
Wed 09/30 04Z 0.02 3406  89  34  10 0.00
Wed 09/30 05Z 0.03 3306  86  31  10 0.00
Wed 09/30 06Z 0.05 3307  86  26  10 0.00
Wed 09/30 07Z 0.04 3308  83  22  10 0.00
Wed 09/30 08Z 0.05 3308  81  18  10 0.00
Wed 09/30 09Z 0.03 3408  72  15  11 0.00
Wed 09/30 10Z 0.04 3309  74  16  11 0.00
Wed 09/30 11Z 0.04 3308  75  18  11 0.00
Wed 09/30 12Z 0.03 3408  73  18  11 0.00
Wed 09/30 13Z 0.03 3307  72  14  11 0.00
Wed 09/30 14Z 0.03 3306  70  14  11 0.00
Wed 09/30 15Z 0.04 3204  67  15  12 0.00
Wed 09/30 16Z 0.07 3005  66  23  11 0.00
Wed 09/30 17Z 0.10 3006  65  30  11 0.00
Wed 09/30 18Z 0.10 3006  62  34  11 0.00
Wed 09/30 19Z 0.09 3005  60  29  12 0.00
Wed 09/30 20Z 0.09 3005  59  24  12 0.00
Wed 09/30 21Z 0.10 2905  58  20  12 0.00
Wed 09/30 22Z 0.12 2805  54  15  12 0.00
Wed 09/30 23Z 0.15 2806  52  13  12 0.00
Thu 10/01 00Z 0.14 2706  51  16  12 0.00
Thu 10/01 01Z 0.16 2606  54  18  12 0.00
Thu 10/01 02Z 0.18 2607  56  18  12 0.00
Thu 10/01 03Z 0.23 2609  64  25  11 0.00
Thu 10/01 04Z 0.25 2610  73  32  11 0.00
Thu 10/01 05Z 0.23 2609  75  43  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.09 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